Method of producing a relief image for printing

ABSTRACT

The present invention involves a method for making a relief image. A film that includes a carrier sheet and an imageable material is used to form a mask image that is opaque to a curing radiation. In one embodiment, the mask image is formed on the carrier sheet while in another embodiment, the mask image is formed on a receptor sheet. The mask image is then transferred to a photosensitive material, such as a flexographic printing plate precursor. The resulting assembly is exposed to the curing radiation resulting in exposed and unexposed areas of the photosensitive material. The carrier sheet or the receptor sheet may be removed from the mask image either before or after exposure to the curing radiation. Finally, the photosensitive material and mask image assembly is developed with a suitable developer to form a relief image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims the benefit of U.S.application Ser. No. 11/081,018, titled “Method of Producing a ReliefImage for Printing” filed Mar. 15, 2005 now U.S. Pat. No. 8,142,987, andclaims the benefit of Provisional Application Ser. No. 60/561,162,titled “Method of Producing a Relief Image for Printing” filed Apr. 10,2004 and claims the benefit of Provisional Application 60/630,460, alsotitled “Method of Producing a Relief Image for Printing” filed Nov. 23,2004, each of which are hereby incorporated by reference.

BACKGROUND

This invention is directed to methods of making an article bearing arelief image by forming a mask image from a film, transferring the maskimage to a photosensitive material, and exposing the photosensitivematerial to a curing radiation. Photosensitive elements comprising alaser-ablatable mask layer on the surface of a photosensitive elementhave been reported. Such elements may be made into articles bearing arelief image without the use of a digital image negative or otherseparate masking device. The photosensitive elements having an ablatablemask layer (or a so-called “integral mask”) can be imaged by firstimagewise exposing the photosensitive element with laser radiation(generally from an infrared laser under computer control) to selectivelyremove the mask layer in the exposed areas, and then overall exposingwith an actinic radiation to cure the photosensitive layer in theunmasked areas. The remaining areas of the mask layer and thenon-hardened portions of the photosensitive layer are then removed byone or more liquid development processes. Examples of flexographicarticles having an ablatable mask layer are described in U.S. Pat. No.5,262,275 to Fan, U.S. Pat. No. 5,705,310 to Van Zoeren, U.S. Pat. No.5,719,009 to Fan, U.S. Pat. No. 6,020,108 to Goffing, et al., and U.S.Pat. No. 6,037,102 to Loerzer, et al.

While elements having a laser-ablatable mask layer allow directimagewise exposure with a laser and do not require a separate maskingdevice, the imaging time to create the mask is very long since thesensitivity to infrared radiation is low for the known integral masksystems. Sensitivity is generally not lower than about 1 J/cm², andtypically about 3 J/cm² is required for laser-ablation imaging.

In recent years attempts have been made, such as reported in U.S. Pat.No. 6,521,390 to Leinenbach, et al., to improve the infrared sensitivityof an ablatable mask layer by using heat-combustible polymeric bindersand specific aliphatic diesters. Although higher sensitivity and, assuch, shorter exposure time may be achieved, this construction suffersfrom undesirable adhesion of the ablatable mask layer to a coversheetthat must be removed before exposure; see U.S. Pat. No. 6,599,679 toPhilipp, et al. at C1 and C2, Table 2.

Higher sensitivity is difficult with the integral-mask construction asthe laser-ablatable layer must satisfy a number of widely varyingquality criteria; see U.S. Pat. No. 6,599,679, col. 2, line 1-29. Theuse of a polyether-polyurethane binder in an ablatable layer is reportedin U.S. Pat. No. 6,599,679, but the enhancement in imaging speed wasmodest (Examples 1-3 reported at Table 2; cf. Comparative Example C6).

Furthermore, the integral-mask approach for the production offlexographic printing plates requires the use of high-poweredlaser-equipped imagers specifically configured for imaging theflexographic articles, such as CYREL Digital Imager (CDI SPARK)manufactured by Esko-Graphics (Kennesaw, Ga.), and ThermoFlex by Creo(Burnaby, British Columbia). Because of the need for varying thethicknesses of a flexographic plates depending upon the specificprinting application, more than one imager may be required with theintegral-mask approach.

In contrast, conventional imaging apparatus for “computer-to-plate”lithographic applications (e.g., TRENDSETTER from Creo), and digitalproofing applications (e.g., DESERTCAT 88 from ECRM) may be used in thepresent invention that use the film to make a mask image.

SUMMARY OF THE INVENTION

In one embodiment, the method includes the steps of providing a filmthat includes an imageable material disposed on a carrier sheet; forminga mask image on the carrier sheet by producing exposed and non-exposedareas of the imageable material; transferring the mask image to aphotosensitive material that is sensitive to a curing radiation suchthat the imageable material adheres more to the photosensitive materialthan to the carrier sheet; exposing the photosensitive material to thecuring radiation through the mask image to form an imaged article,wherein the mask image is substantially opaque to the curing radiation;and developing the imaged article to form the relief image.

In another embodiment, the mask image is formed on the receptor sheet,rather than on the carrier sheet. In this embodiment, the methodincludes the steps of contacting the imageable material of the film witha receptor sheet so that the mask image is formed on the receptor sheetby transferring exposed areas of the imageable material to the receptorsheet and removing the carrier sheet from the mask image. Followingthese steps, the mask image is transferred to a photosensitive material,exposed to the curing radiation and developed to form a relief image.

In still another embodiment, the method includes the steps of forming amask image on a carrier sheet by producing exposed and non-exposed areasof a film; transferring the mask image to a photosensitive material thatis sensitive to a curing radiation such that the imageable materialadheres more to the photosensitive material than to the carrier sheet;exposing the photosensitive material to the curing radiation through themask image to form an imaged article, wherein the mask image issubstantially opaque to the curing radiation; and developing the imagedarticle to form the relief image.

In yet another embodiment, a mask image is formed on the carrier sheetby producing exposed and non-exposed areas of the imageable material andis then transferring to a photosensitive material that is sensitive to acuring radiation. In this embodiment, the carrier sheet is removed fromthe mask image before the step of exposing the photosensitive materialto the curing radiation.

In another embodiment, the method includes forming a mask image, from afilm that includes a carrier sheet, a release layer disposed on thecarrier sheet and an imageable material disposed on the release layer.In this embodiment, the imageable material includes a thermally adhesivebinder. The mask image is then transferred to a photosensitive materialsuch that the mask image is more adhesive to the photosensitive materialthan to the carrier sheet. Following transfer, the photosensitivematerial is exposed to the curing radiation through the carrier sheetand the mask image to form an imaged article. This exposure step isperformed without vacuum pressure. Finally, the carrier sheet from themask image and the mask image and the imaged article are developed toform the relief image.

Issues related to handling, mounting, and spinning in drum-based imagingsystems of thick flexographic articles (with associated tendency forcracking, fingerprinting, etc.) may be avoided by using the method ofthe present invention. For example, if the photosensitive material is athick flexographic article, the flexographic article may be cured whileremaining substantially flat after the mask image is transferred to theflexographic article.

Yet another advantage of the invention is that the mask image may beexamined prior to transferring the mask image to the photosensitivematerial. This permits the mask image to be “proofed” and correctedbefore a relief image is produced. Since the photosensitive material istypically much more expensive than the film used for making the maskimage, cost savings can be realized in the production of flexographicprinting plates.

The method of the present invention is advantageous as compared toimageable articles with “integral masks”. For example, the mask imagemay be made from a film in significantly less time than when anintegral-mask article is imaged, due to much greater imagingsensitivity. In some embodiments, for example, only about 0.5 J/cm² isrequired for mask imaging, resulting in greatly increased throughput.

A transferable mask provides flexibility in production, since atransferable mask can be used in combination with a variety ofphotosensitive materials and can therefore be used in a variety ofapplications. A transferable mask can also be used in combination withcommercially available photosensitive materials on an as-needed basis.In contrast, integral-mask articles must be used with the underlyingflexographic substrate, and so must be specifically manufactured for thedesired application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E schematically illustrate an embodiment of the invention thatincludes:

(1A) digitally creating a mask image from a film comprising a carriersheet and a layer of imageable material;

(1B) laminating the mask image onto a flexographic precursor comprisinga photosensitive layer and separation layer on a substrate;

(1C) removing the carrier sheet from the mask image;

(1D) exposing the flexographic precursor to curing radiation; and

(1E) developing the flexographic precursor to provide a flexographicprinting plate bearing a relief image.

FIG. 2 illustrates the reduced imaging energy requirement attained byforming a mask image according to the invention. “TOD” refers to thetransmission optical density (for ultraviolet radiation) of the exposedareas of a film. Only about 0.5-0.7 J/cm² is required to achievesufficient transparency for effective masking.

FIGS. 3A-3E schematically illustrate a method of the invention thatincludes:

(3A) digitally creating a mask image from a film comprising a carriersheet and a layer of imageable material;

(3B) laminating the mask image onto a flexographic precursor comprisinga photosensitive layer and separation layer on a substrate;

(3C) exposing the flexographic precursor to curing radiation;

(3D) removing the carrier sheet from the mask image; and

(3E) developing the flexographic precursor and mask image to provide aflexographic printing plate bearing a relief image.

FIG. 4A illustrates a cross-sectional view of one embodiment of the filmthat includes a carrier sheet, a release layer, a barrier layer and animageable material.

FIG. 4B illustrates a cross-sectional view of one embodiment of aphotosensitive material disposed on a substrate prior to transfer of themask image to the photosensitive material.

FIG. 5A illustrates an image of the type produced by the flexographicplate formed in Example 1.

FIG. 5B illustrates an image of the type produced by the flexographicplate formed in Example 2.

FIG. 6A illustrates an image of the 30% dots produced by theflexographic plate formed in Example 1.

FIG. 6B illustrates an image of the 30% dots produced by theflexographic plate formed in Example 2.

FIG. 7A illustrates four-point Helvetica type printed by a flexographicplate produced with the method of the present invention.

FIG. 7B illustrates four-point Helvetica type printed by a flexographicplate produced with a known flexographic plate with an integral mask.

FIG. 8A illustrates 80 micrometer fine line printed by a flexographicplate produced with the method of the present invention.

FIG. 8B illustrates 80 micrometer fine line printed by a flexographicplate produced with a known flexographic plate with an integral mask.

FIG. 9A illustrates 25% dots in a 150 lpi Silver Halide mask (88% to 90%UV-A transmission).

FIG. 9B illustrates 25% dots in a 150 lpi integral mask (73% to 78% UV-Atransmission).

FIG. 9C illustrates 25% dots in a 150 lpi transfer mask (95% to 98% UV-Atransmission).

FIG. 10A illustrates an image of 4-point type produced in theflexographic plate of Example 7.

FIG. 10B illustrates an image of 4-point type produced in theflexographic plate of Example 8.

FIG. 11A illustrates a photomicrograph of reversed 3-point type producedin the flexographic plate of Example 7.

FIG. 11B illustrates a photomicrograph of 3-point type produced in theflexographic plate of Example 8.

FIG. 12A illustrates a measured line width of 56 micrometers for a lowercase L in four-point Helvetica type printed by first flexographic plate.

FIG. 12B illustrates a measured line width of 78 micrometers for alower-case L in four-point Helvetica type printed by the secondflexographic plate.

DETAILED DESCRIPTION OF THE INVENTION

The steps of the inventive method and the components used in this methodare described further below.

Film

In the method of the present invention, a film is used to form a maskimage on the carrier sheet. One step of the method includes providing afilm comprising an imageable material and a carrier sheet. The imageablematerial is generally disposed on the carrier sheet as a relativelyuniform coating of one or more layers. The film may optionally includeone or more additional layers, such as a barrier layer, a release layer,an adhesive layer, or other layers. Different constructions of the filmmay be designed to be imaged one or more imaging methods.

The film generally includes at least two elements—a sheet-formsubstrate, or carrier sheet, and a layer of imageable materialcontaining a binder, an energy absorber, and a colorant disposed on thesubstrate. In a particular embodiment, the binder is an adhesive binder.By using an adhesive binder in the imageable material, the mask imageadheres more to the photosensitive material than to the carrier sheet.Due to the adhesion of the mask image to the photosensitive material,the step of exposing the photosensitive material may be done without thevacuum draw-down that is typically employed in the analog method ofimaging a photosensitive material. When the imageable material ispatternwise exposed to infrared radiation, normally from a scanninginfrared laser source, the radiation is absorbed by the energy absorberwhich causes transfer of the imageable material or the colorant from thecarrier sheet in those imaged areas. The colorant generally providessubstantial opacity to the curing radiation used in a subsequent step ofthe method. This process is outlined in U.S. Pat. No. 5,935,758 toPatel, et al., which is hereby incorporated by reference in itsentirety. Following exposure to radiation and removal of the exposed orunexposed portions of the imageable material, the remaining imageablematerial is referred to as the mask image.

In one embodiment, the film comprises a release layer disposed on thecarrier sheet and an imageable material disposed on the release layer.In another embodiment, illustrated in FIG. 4A, the film 40 comprises arelease layer 46 disposed on a carrier sheet 48, a barrier layer 44disposed on the release layer 46, and an imageable material 42 disposedon the barrier layer 44. If particular types of imaging mechanisms areused, a receptor sheet may then be disposed on the imageable material.The carrier sheet 48, release layer 46, barrier layer 44, imageablematerial 42, and other layers are described further below.

Carrier Sheet

The carrier sheet of the film may be any suitable substrate. Suitablesubstrates include, for example, plastic sheets and films, such aspolyethylene terephthalate or polyethylene naphthalate, fluorenepolyester polymers, polyethylene, polypropylene, acrylics, polyvinylchloride and copolymers thereof, and hydrolyzed and non-hydrolyzedcellulose acetate.

Where imaging radiation is used to create the mask image, it may bedesirable (although not necessary) that the carrier sheet besufficiently transparent to the imaging radiation. In some embodiments,the carrier sheet may be a transparent polymeric film. An example of acommonly employed carrier sheet is a polyethylene terephthalate sheet.Typically, the polyethylene terephthalate sheet is about 20 μm to about200 μm thick. For example, a polyethylene terephthalate sheet sold underthe name MELINEX by DuPont Teijin Films (Hopewell, Va.), such as MELINEX574, is suitable.

If necessary, the carrier sheet may be surface-treated so as to modifyits wettability and adhesion to subsequently applied coatings. Suchsurface treatments include corona discharge treatment, and theapplication of subbing layers or release layers.

Release Layer

The film may contain a release layer disposed between the carrier sheetand the imageable material. The presence of a release layer may bedesirable to facilitate transfer of imageable material to a receptorsheet, or transfer of a resulting mask image to the photosensitivematerial in a subsequent step of the method. Generally, known articlesfor making a mask image may be adapted for use in the methods of thepresent invention by including a release layer disposed between thecarrier sheet and the imageable material.

It is preferable that the release layer can be developable, dispersible,or easily removable after exposure to curing radiation through the maskimage, generally during subsequent processing of the photosensitivematerial. Furthermore, it may be desirable to ensure that the releaselayer does not significantly absorb or scatter the curing radiation.

By way of example only, coatings suitable as a release layer can includepoly(vinyl alcohol) or similar polymers, a cellulosic polymer such asmethylcellulose or hydroxypropyl methylcellulose, or polyvinyl butyralor other hydroxylic polymer as described above. One particular exampleof the release layer is a hydrolized styrene maleic anhydride.

A transparent and thin release layer may be beneficial to obtain ahigher resolution image. The release layer thickness may range fromabout 0.1 micron to 10 micron, for example. A thin release layer may beadvantageous, as a thin layer does not adversely affect the resolutionthat is obtainable for the resulting relief image. A thin release layermay also be easier to remove during subsequent processing steps. It ispreferable not to include beads or other light scattering materials inthe release layer.

In one embodiment the release layer may contain a polymer or mixture ofpolymers that provides a desired oxygen permeability that affects thesubsequent imaging of the photosensitive material, as reported in U.S.Pat. No. 5,248,583 to Lundquist, et al. for example. In theseembodiments, the release layer is transferred to the photosensitivematerial (along with the mask image) as a fairly continuous layer. For arelease layer having low oxygen permeability, curing could be moreefficient to provide durability and ink receptivity. Whereas, for arelease layer having higher oxygen permeability, better dot sharpnessmay be obtained due to reduced curing at the surface of the reliefimage. A thin release layer comprising a polymer having low oxygenpermeability, such as methylcellulose, may provide the optimumperformance of cure and dot sharpness.

In another embodiment, the release layer for a thermal ablative imagingsystem is a thermally resistant polymer layer. A thermally resistantpolymer for the release layer is beneficial for maintaining theintegrity of the release layer, and maintains good release propertieseven after thermal imaging. Thermal resistant polymers, such aspolyimides, polysulfones, polyether ether ketone (PEEK), bisphenol-Aterephthalate, polyvinyl alcohols, and polyamides are useful, providedthe chosen polymer gives good release from the carrier sheet, and alsocan be developable, dispersible, or easily removable after exposure tocuring radiation during subsequent processing of the photosensitivematerial.

The release layer may also comprise a crosslinking agent to providebetter release properties. The release layer may also contain coatingaids, surfactants, release-enhancing materials, etc. For example, therelease layer may contain a suitable surfactant such as SURFYNOL 465(ethoxylated tetramethyl decynediol) or SURFYNOL GA (acetylenic diolscompounded with other non-ionic surfactants and solvents) from AirProducts (Allentown, Pa.), SURFACTOL 365 (ethoxylated castor oil), fromCasChem. Inc. (Bayonne, N.J.) or Triton X-100(octylphenoxypolyethoxyethanol) from Rohm & Haas (Philadelphia, Pa.).

Barrier Layer

The film may also contain a barrier layer disposed between the carriersheet and the imageable material. A barrier layer may be particularlysuitable when the imaging method includes an ablative mechanism, forexample.

Suitable barrier layers and their preparation are described, forexample, in U.S. Pat. Nos. 5,468,591 and 5,576,144 to Pearce, et al.,and U.S. Pat. No. 6,369,844 to Neumann, et al. The barrier layer mayinclude a binder, and more particularly, a “heat-combustible” binder.Suitable heat-combustible binders are reported in U.S. Pat. No.6,521,390 to Leininbach, et al. By way of example only, suitableheat-combustible binders include poly(alkyl cyanoacrylate) andnitrocellulose. Propellant-generating polymers, such as glycidyl azidepolymer (“GAP”), and other azido group-containing polymers are describedin U.S. Pat. No. 5,278,023 to Bills, et al. and U.S. Pat. No. 6,027,849to Vogel.

The barrier layer may comprise a particulate material such as metaloxide particles. One suitable particulate material for use in thebarrier layer is an iron oxide particulate available from Toda KogycoCorp., (Hiroshima, Japan). Particulate materials may provide highoptical density with respect to imaging or curing radiation. Metal oxideparticulates may be advantageous for an ablative imaging mechanismbecause they can thermally decompose to generate propulsive gases. Othersuitable particulates and metal oxide particulates are reported in U.S.Pub. App. 2001/0026309, for example.

The barrier layer may optionally comprise an infrared-absorbing dye. Thepreferred infrared-absorbing dyes for the barrier layer are cationicinfrared-absorbing dyes reported in U.S. Pat. No. 5,935,758.Particularly suitable infrared-absorbing dyes arephotothermal-bleachable dyes.

The barrier layer may also comprise a crosslinking agent. The use of acrosslinking agent may impart greater thermal resistance to the barrierlayer. Exemplary crosslinking agents include melamine-formaldehyderesins, such as RESIMENE from UCB Group (Belgium), dialdehydes such asglyoxal, phenolics such as DURITE from Borden Chemical Inc. (Columbus,Ohio), polyfunctional aziridines, isocyanates such as DESMODUR AP fromBayer Corp. (Pittsburgh, Pa.), urea-formaldehyde, epoxies such as EPON1001 from Shell Chemical (Houston, Tex.). Many other suitablecrosslinking agents are known in the art.

Imageable Material

The imageable material is generally disposed on the carrier sheet as arelatively uniform coating (i.e., substantially continuous and having afairly uniform thickness). In some embodiments, the imageable materialresides on the carrier sheet as a single layer. In other embodiments,the imageable material may comprise more than one layer, depending onthe chosen imaging method. For example, the imageable material mayinclude a light-to-heat converting layer, containing an energy absorber,and a layer comprising ablative or sublimable material on top of thelight-to-heat converting layer.

Preferably, the components of the imaging material are chosen such thatthe mask image is soluble or swellable in a developer solution that issubsequently used to create the relief image, or removable by some othermeans, after exposure of the photosensitive material to curableradiation through the mask.

The imageable material may include a colorant. Generally, the colorantwill be present in the resulting mask image, and will be capable ofproviding strong absorbance of the curing radiation or is otherwisecapable of blocking the curing radiation, such as by reflectance. Asused herein, the term “colorant” indicates a component thatsubstantially prevents the transmission of curing radiation through themask image. The term “colorant” does not indicate that the componentnecessarily provides or imparts a visible color to the imageablematerial, although it may do so.

The colorant generally comprises one or more dyes or pigments that willprovide the desired spectral properties. The colorant is preferablypresent in the imageable material in an amount of about 10-50 wt %,based on the solids content of the imageable material.

The colorant can be a particulate material that is of sufficiently smallparticle size to be dispersed within the imageable material, with orwithout the aid of a dispersant. Suitable colorants for use in theimageable material include pigments, nonsublimable dyes, or sublimabledyes. Pigments and nonsublimable dyes are suitably employed because theydo not tend to migrate. The use of pigment dispersions in imaging iswell-known in the art, and any conventional pigments useful for thatpurpose may be used in the present invention.

In one embodiment of the invention, the colorant is a black dye orpigment. A suitable black dye or pigment absorbs energy at substantiallyall wavelengths across the visible spectrum, for example, between about350-750 nm. However, the black dye or pigment may, for example, alsoabsorb in the infrared or ultraviolet region as well. Suitable blackdyes or pigments may also include dyes and pigments that absorbdifferent wavelengths within the visible spectrum. These dyes orpigments may, for example, actually be a deep blue or other color. Theblack dye or pigment may include mixtures of dyes or pigments, ormixtures of both dyes and pigments, that individually may or may not beblack but when mixed together provide a neutral black color.

For example, a mixture of NEPTUN Black, Blue Shade Magenta, and RedShade Yellow Pigment, available from BASF (Germany), which provide aneutral black color, may be suitable. DISPERCEL CBJ from RunnemadeDispersions KV (United Kingdom) may also be suitable as the colorant.

One suitable black pigment is carbon black. Carbon black exhibitsneutral color and suitable covering power. It may be desirable to use acarbon black having small particles for maximum color strength.Fine-grained carbon black brands with a mean particle size below 30 nmare especially suitable. Examples of suitable carbon black pigmentsinclude RAVEN 450, 760 ULTRA, 890, 1020, 1250, and others available fromColombian Chemicals Co. (Atlanta, Ga.), as well as BLACK PEARLS 170,BLACK PEARLS 480, VULCAN XC72, BLACK PEARLS 1100, and others availablefrom Cabot Corp. (Waltham, Mass.). Other suitable carbon blacks includePRINTEX U, PRINTEX L6, SPEZIALSCHWARZ 4 OR SPEZIALSCHWARZ 250 of Degussa(Germany). The carbon black may comprise, for example, about 10-50 wt %,more particularly about 10-40 wt %, and even more particularly about10-30 wt % of the total weight of the imageable material.

Imageable materials containing only carbon black are difficult toformulate due to inherent absorption of infrared radiation by the carbonblack particles. Overheating of the carbon black within the imageablematerial may result in loss of density or increased diffusion of themask image. Diffusion of the mask image may cause poor edge sharpness ofthe final imaged article. Incorporating one or more non-infraredabsorbing black dyes or pigments in combination with carbon black, intothe imageable material reduces the interference with the radiation andimproves the quality of the imaged article that results. Even though theconcentration of carbon black is reduced significantly, suitable colorneutrality and opacity is maintained.

Also suitable as a pigment is a non-carbonaceous particulate materialsuch as metal particles or metal oxide particles.

In another embodiment of the invention, the colorant may be anon-infrared absorbing black dye or pigment. Non-infrared absorbingblack dyes or pigments include dyes or pigments that absorb minimal orno amount of infrared radiation.

In this embodiment, a mask image is created using an imaging radiationin the infrared region, which is absorbed by a separate infraredabsorber. The colorant then would be opaque to (or reflective of) thecuring radiation, which is generally ultraviolet radiation. Thenon-infrared absorbing colorant may absorb some infrared radiation inthis embodiment, as long as there is little or no interference with theinfrared absorber. For example, non-infrared absorbing black dyes orpigments may absorb less than about 0.5 absorbance unit, moreparticularly, less than about 0.1 absorbance unit of infrared radiation,at use concentrations.

Non-infrared absorbing black dyes and pigments include, for example,NEPTUN Black X60, PALIOGEN Black S 0084, available from BASF (Germany),as well as MICROLITH Violet B-K, available from Ciba Specialty Chemicals(Tarrytown, N.Y.). Other suitable non-infrared absorbing black dyes maybe found in U.S. Pat. No. 6,001,530 to Kidnie, et al. which isincorporated herein by reference in its entirety.

In another embodiment, the imageable material may include anultraviolet-absorbing dye as a colorant. The dye typically has a strongabsorbance in the region of the spectrum to which the photosensitivematerial is sensitive and which is used as the curing radiation foroverall exposure. The ultraviolet-absorbing dye may have an absorbancemaximum in the range of about 250-600 nm, more typically between about300-500 nm. Developer-soluble dyes are preferred. Examples of such dyesare reported in U.S. Pat. No. 3,769,019 to Weise, et al., U.S. Pat. No.4,081,278 to Dedinas, et al. and, U.S. Pat. No. 5,399,459 to Simpson, etal. Examples of suitable ultraviolet-absorbing dyes include thosemarketed under the name UVINUL from BASF (Germany), and KEYPLAST YELLOWGC from Keystone Aniline Corporation (Chicago, Ill.).

The imageable material may also include an energy absorber. Excitationof the energy absorber by imaging radiation initiates a transfer ofcolorant or imageable material, or a physical or chemical change thatalters the transparency or opacity of the imageable material to curingradiation. In some embodiments, the colorant acts as the energyabsorber, and inclusion of a separate energy absorber is not required.In other words, for these embodiments the colorant serves a dualfunction. In other embodiments, however, a separate energy absorber ispresent which sensitizes the imageable material to an imaging radiation.

In one embodiment, the energy absorber may include an infrared absorber.The infrared absorber may, for example, convert infrared radiation toheat. The infrared radiation may be, for example, in the range of750-1200 nm. The generation of heat in the imageable material may thenresult in a physical or chemical change in the other components of theimageable material, or induce ablation. Examples of suitable infraredabsorbers include infrared-absorbing dyes such as cyanineinfrared-absorbing dyes, infrared-absorbing pigments such as carbonblack, or metals such as aluminum.

In some embodiments, the infrared-absorbing dye is a cationic dye.Suitable cationic dyes for use in the transfer material of the presentinvention include tetraarylpolymethine (TAPM) dyes, amine cation radicaldyes, and mixtures thereof. Preferably, the dyes are thetetraarylpolymethine dyes. Dyes of these classes are typically stablewhen formulated with the other components of the imageable material andother layers of the film, and absorb in the correct wavelength rangesfor use with the commonly available laser sources. Furthermore, dyes ofthese classes are believed to react with a latent crosslinking agent,described below, when photoexcited by laser radiation.

TAPM dyes comprise a polymethine chain having an odd number of carbonatoms (5 or more), each terminal carbon atom of the chain being linkedto two aryl substituents. TAPM dyes generally absorb in the 700-900 nmregion, making them suitable for diode laser address. Suitable TAPM dyesare described, for example, in U.S. Pat. No. 5,935,758 to Patel, et al.

Suitable cationic infrared-absorbing dyes include the class of aminecation radical dyes (also known as immonium dyes) reported, for example,in International Publication WO 90/12342, and in EP publication 0 739748. Suitable cationic infrared-absorbing dyes are also described inU.S. Pat. No. 5,935,758 to Patel, et al.

The infrared-absorbing dye is preferably present in a sufficientquantity to provide a transmission optical density of at least about0.5, more preferably, at least about 0.75, and most preferably, at leastabout 1.0, at the exposing wavelength. Typically, this is achieved withabout 3-20 wt % infrared-absorbing dye, based on the solids content ofthe imageable material. The infrared-absorbing dye should be sufficientto produce substantially transparent areas where the imageable materialis exposed to infrared radiation. The term “substantially transparent”means that the unmasked areas of the photosensitive material should havea transmission optical density of about 0.5 or less, more particularlyabout 0.1 or less, even more particularly about 0.05 or less. Thetransmission optical density may be measured using a suitable filter ona densitometer, such as, for example a MACBETH TR 927.

FIG. 2 illustrates the amount of energy and the amount ofinfrared-absorbing dye that is required to produce substantiallytransparent areas on the carrier sheet or receptor sheet. The graphshows the average transmission optical density (“TOD”) of the exposedareas on the y-axis and the energy in J/cm² required to achieve that TODon the x-axis. The various symbols illustrate the wt % ofinfrared-absorbing dye used in the imageable material. The diamondindicates the coordinates for an imageable material that contains 12.1wt % in grams of infrared-absorbing dye. The square indicates thecoordinates for an imageable material that contains 17.2 wt % in gramsof infrared-absorbing dye. The triangle indicates the coordinates for animageable material that contains 17.2 wt % in grams ofinfrared-absorbing dye.

In another embodiment, the energy absorber may include an ultravioletabsorber. The ultraviolet absorber may absorb radiation in the range ofabout 150-400 nm, for example.

The imageable material may also include a binder. Suitable binders arecapable of dissolving or dispersing the other components included in theimageable material. The binder may serve several purposes depending onthe imaging system.

One function of the binder is to aid in the subsequent transfer of theresulting mask image to the photosensitive layer. A binder that providesthermoplastic properties may ease the transfer of the mask image to thephotosensitive material. A binder that provides better adhesion to thephotosensitive material may also be helpful.

The total binder is typically present in an amount of about 25-75 wt %,and more suitably in an amount of about 35-65 wt %, based on the solidscontent of the imageable material.

A wide variety of binders may be suitable in the practice of theinvention, with the choice of binder depending on the selected imagingmethod. The binder should be compatible with the other selectedcomponents of the imageable material, and should be soluble in asuitable coating solvent such as lower alcohols, ketones, ethers,hydrocarbons, haloalkanes and the like. By including an adhesive binderin the imageable material, the mask image becomes more adhesive to thephotosensitive material following transfer of the mask image to thephotosensitive material.

In one embodiment, the binder includes an adhesive binder. Adhesivebinders are known in the art and any may be used in the method of thepresent invention. Particularly suitable adhesive polymers includethermally adhesive binders, for example those with a glass transitiontemperature (Tg) of less than about 65° C., more particularly less thanabout 60° C. Some examples of suitable adhesive binders include acetylpolymers and acrylamide polymers. One example of a commerciallyavailable acetyl polymer is BUTVAR B-76 from Solutia, Inc. (St. Louis,Mo.). Other binders from the BUTVAR series of polymers may also be used.One example of a commercially available acrylamide polymer is MACROMELT6900 from Henkel Corp. (Gulph Mills, Pa.). Pressure-sensitive adhesivebinders may also be suitable. Such binders are generally known in theart.

The binder may be a polymeric material that contains a plurality ofhydroxy groups (i.e., a “hydroxylic polymer”). In one embodiment, 100%of the binder is a hydroxylic polymer. The hydroxy groups may bealcoholic groups or phenolic groups, or both. Binders comprisingpredominantly alcoholic groups are suitable. A hydroxylic polymer may beobtained by polymerization or copolymerization of hydroxy-functionalmonomers such as allyl alcohol and hydroxyalkyl acrylates ormethacrylates, or by chemical conversion of preformed polymers, e.g., byhydrolysis of polymers and copolymers of vinyl esters such as vinylacetate. Polymers with a high degree of hydroxy functionality, such aspoly(vinyl alcohol), cellulose, etc., are in principle suitable for usein the invention, but in practice the solubility and otherphysico-chemical properties are less than ideal for most applications.Derivatives of such polymers, obtained by esterification,etherification, or acetalization of the bulk of the hydroxy groups,generally exhibit superior solubility and film-forming properties, andprovided that at least a minor proportion of the hydroxy groups remainunreacted, they are suitable for use in the invention.

One suitable hydroxylic polymer for use as the binder is a reactionproduct formed by reacting poly(vinyl alcohol) with butyraldehyde.Commercial grades of this reaction product typically leave at least 5%of the hydroxy groups unreacted (i.e., free), and are generally incommon organic solvents and possess excellent film-forming andpigment-dispersing properties.

A commercially available hydroxylic polymer that is suitable is apolyvinyl butyral polymer available under the trade designation BUTVARB-76 from Solutia, Inc. (St. Louis, Mo.). This particular polymer has asoftening range of about 140°-200° C. Other hydroxylic binders from theBUTVAR series of polymers may also be used. Polyvinyl butyral polymersavailable under the trade designations MOWITAL from Kuraray America,Inc. (New York, N.Y.) are also suitable.

Alternatively, a blend of one or more non-crosslinkable binders with oneor more hydroxy-functional binders may be used. A non-crosslinkablebinder should be compatible with the imaging system of the presentinvention such that it does not interfere with the transfer of colorant.That is, it should be nonreactive when exposed to the conditions usedduring imaging. Suitable non-crosslinkable binders include, for example,polyesters, polyamides, polycarbamates, polyolefins, polystyrenes,polyethers, polyvinyl ethers, polyvinyl esters, polyacrylates,polymethacrylates, and the like. An example of a suitable commerciallyavailable non-crosslinkable binder that can be combined with thehydroxylic binders described above in the imageable material includespoly(methyl methacrylate) available under the trade designation ELVACITEfrom DuPont (Wilmington, Del.).

Binder-free imageable materials are also possible, as reported inInternational Publication WO 94/04368.

The imageable material may optionally include a fluorocarbon additivefor enhancing transfer of a molten or softened film and production ofhalftone dots (i.e., pixels) having well-defined, generally continuous,and relatively sharp edges. Under imaging conditions, it is believedthat the fluorocarbon additive serves to reduce cohesive forces withinthe imageable material at the interface between the laser-exposed heatedregions and the unexposed regions, and thereby promotes clean “shearing”of the exposed regions in the direction perpendicular to the majorsurface of the imageable material. This provides improved integrity ofthe dots with sharper edges, as there is less tendency for “tearing” orother distortion as the exposed regions separate from the rest of theimageable material.

A wide variety of compounds may be employed as the fluorocarbonadditive, provided that the chosen additive is substantially involatileunder normal coating and drying conditions, and is sufficientlycompatible with the binder(s). Thus, highly insoluble fluorocarbons,such as polytetrafluoroethylene and polyvinylidenefluoride, areunsuitable, as are gases and low boiling liquids, such asperfluoralkanes. With the above restrictions, both polymeric and lowermolecular weight materials may be used.

Examples of suitable fluorocarbon additives are described in U.S. Pat.No. 5,935,758 to Patel, et al. The imageable material may also include afluorocarbon compound as described in U.S. Pat. No. 6,664,020 to Warner,et al. Other suitable fluorocarbon compounds are reported in EPpublication 0 602 893 and the references cited therein. A preferredfluorocarbon additive is a sulfonamido compound N-ethylperfluorooctanesulfonamide having the formula (C₈F₁₇)SO₂NH(CH₂CH₃),which includes 70% straight chains and 30% branched chains. Thefluorocarbon additive is typically used in an amount of about 1-10 wt %,based on the dry coating weight of the imageable material. Preferably,the weight ratio of fluorocarbon additive to colorant is at least about1:10, and more preferably at least about 1:5.

A latent crosslinking agent is employed in some embodiments. A latentcrosslinking agent may be especially suitable when a LIFT system isemployed as the imaging mechanism. As used herein, a “latentcrosslinking agent” is a compound that is capable of causingcrosslinking only under conditions of laser address. It is believed thatduring laser imaging, the latent crosslinking agent reacts with aphotoexcited infrared absorbing dye, which initiates crosslinking of thehydroxylic binder. Thus, crosslinking occurs during laser imaging.

Suitable latent crosslinking agents include compounds derived fromdihydropyridine, for example. Suitable derivatives of dihydropyridinecan be substituted at any of the ring positions with appropriatesubstituents, such as alkyl or aryl groups. In particular,3,5-dicarboxylic diester derivatives of dihydropyridine are suitable aslatent crosslinking agents. Polymers comprising a 3,5-dicarboxylicdiester derivative of dihydropyridine integrated into the polymerbackbone may also be suitable. Latent crosslinking agents that areuseful in the imageable material are described in U.S. Pat. No.5,935,758 to Patel, et al.

This latent crosslinking agent is present in the imageable material inan amount of up to about 30 wt %, based on the solids content of theimageable material. Alternatively, a latent crosslinking agent can bepresent in a receptor sheet.

The latent crosslinking agent is believed to be important for providingcohesion within the transferred colorant. This complements the action ofa fluorocarbon additive, and results in transfer of the exposed regionas a coherent film. It is also believed to be important for preventingretransfer of colorant back to the film, as well as back-transfer ofcolorant to a separate film in a subsequent imaging step.

Additional components such as, for example, plasticizers, coating aids,dispersing agents, UV absorbers, fillers, etc., can also be incorporatedinto the imageable material. The various additives are well-known in theart.

The imageable material may also contain, for example, a coating aid.Dispersing agents, or “dispersants,” may be desirable to achieve optimumdispersion quality. Some examples of dispersing agents include, forexample, polyester/polyamine copolymers, alkylarylpolyether alcohols,acrylic binders, and wetting agents. One suitable dispersant in theimageable material is a block copolymer with pigment-affinic groups,which is available under the trade designation DISPERBYK 161 fromByk-Chemie USA (Wallingford, Conn.). The dispersing agent is preferablyused in the dispersion in an amount of about 1-6 wt %, based on thesolids content of the imageable material.

Surfactants may be used as a coating aid to improve solution stability.A wide variety of surfactants can be used. One suitable surfactant is afluorocarbon surfactant used in the imageable material to improvecoating quality. Suitable fluorocarbon surfactants include fluorinatedpolymers, such as the fluorinated polymers described in U.S. Pat. No.5,380,644 to Yonkoski, et al. An example of a suitable coating aid is aNOVEC fluorosurfactant available from 3M (St. Paul, Minn.), such as FC4432. A suitable quantity may be in the range of about 0.05 wt %, andless than about 5 wt %, and typically is in the range of about 1-2 wt %.

Adhesive Layer

The film may also include, as a separate layer generally overlying theimageable material, an adhesive layer. The adhesive layer enhances theadhesion of the mask image to the photosensitive material duringtransfer, and thus aids in the transfer of the mask image. The adhesivelayer may comprise a thermoplastic, thermal adhesive, orpressure-sensitive adhesive, for example. Suitable adhesives are knownin the art.

Receptor Sheet

A receptor sheet is employed in some embodiments of the invention. Asused herein, the phrase “receptor sheet” refers to a material, generallyin sheet-form, having at least one major surface that is capable ofreceiving imageable material from the film.

In some embodiments, the receptor sheet acts only to receive wasteimageable material from the film, and is subsequently discarded. Forthese embodiments, no particular construction of the receptor sheet isrequired; the only requirement is that it is capable of receivingimageable material.

In other embodiments of the invention, however, the receptor sheet has amajor surface capable of imagewise accepting imageable material orcolorant transferred from the film in transfer imaging. For theseembodiments, the receptor sheet includes a sheet support having animage-receiving side and a non-imaging side.

The image-receiving major surface is generally treated or coated tofacilitate the acceptance and fixation of the transferred imageablematerial or colorant. As necessary, the receptor sheet may have acoating on the image-receiving side of the support, having a thicknessin the range of about 2-20 μm. Alternatively, the coating has a coatingweight in the range of about 2-20 g/m².

The sheet support for the receptor sheet is chosen based on theparticular imaging application. Suitable sheet supports include paper orcard stock, metals (e.g., steel or aluminum), or films or platescomposed of various film-forming polymers. Suitable polymeric materialsinclude addition polymers (e.g., poly(vinylidene chloride), poly(vinylchloride), poly(vinyl acetate), polystyrene, polyisobutylene polymersand copolymers), and linear condensation polymers (e.g., polyesters suchas poly(ethylene terephthalate), poly(hexamethylene adipate), andpoly(hexamethylene adipamide/adipate)). The sheet support may betransparent or opaque. Nontransparent sheet supports may be diffuselyreflecting or specularly reflecting.

Suitable sheet supports for the receptor sheet include, for example,plastic sheet materials and films, such as polyethylene terephthalate,fluorene polyester polymers, polyethylene, polypropylene, acrylics,polyvinyl chloride and copolymers thereof, and hydrolyzed andnon-hydrolyzed cellulose acetate. A particularly suitable support is apolyester film, such as a polyethylene terephthalate sheet. For example,a polyethylene terephthalate sheet sold under the name MELINEX by DuPontTeijin Films (Hopewell, Va.), such as MELINEX 574, is suitable.

In practice, the sheet support is typically about 20-200 μm thick. Ifnecessary, the support may be pretreated so as to modify its wettabilityand adhesion to subsequently applied coatings. Such surface treatmentsinclude corona discharge treatment, and application of subbing layers orrelease layers. The sheet support may also comprise a strippable layercontaining an adhesive, such as an acrylic or vinyl acetate adhesive.

Although it is not required, it may be advantageous to include atexturized surface on the image-receiving side of the receptor sheet ofthe present invention. A texturized surface on the sheet support or thecoating may be provided by a plurality of protrusions extending from amajor surface of the support or coating. The protrusions can be obtainedin a variety of ways. For example, a texturizing material may beincluded in the coating to form the protrusions, as discussed below.Alternatively, the sheet support may be microreplicated by conventionalmethods, thereby forming the protrusions. A texturized receptor sheet isreported in U.S. Pat. No. 4,876,235 to DeBoer, for example.

The coating may comprise a binder capable of providing a tack-freesurface at ambient temperatures, and which is compatible with thematerial that will be transferred from the film (such as the imageablematerial or colorant). The coating may contain optional additives suchas surfactants, and antioxidants. The coating may also contain atexturizing material.

In choosing a polymeric binder, considerations include, for example, theglass transition temperature, softening point, and viscosity of thepolymer, etc. A wide variety of polymeric binders are suitable for thepractice of the present invention. The binder may include a hydroxylicpolymer (i.e., a polymer having a plurality of hydroxy groups), or mayinclude polymers free from hydroxy groups.

The choice of the polymeric binder for the coating on the receptor sheetmay depend on the mechanism of colorant transfer involved (e.g.,ablation, melt-stick, or sublimation). For use in an imaging systememploying a melt-stick mechanism, for example, it may be advantageous toemploy a similar or identical binder for the receptor sheet as is usedas the binder of the imageable material on the film.

For some embodiments, BUTVAR B-76 polyvinyl butyral copolymer fromSolutia, Inc. (St. Louis, Mo.) and similar thermoplastic polymers arehighly suitable materials for use in the coating on the receptor sheet.Another suitable polymer for use in the coating of the receptor sheet isa polyvinyl pyrrolidone/vinyl acetate copolymer binder available underthe trade designation E-735 from International Specialty Products, Inc.(Wayne, N.J.). Another suitable polymer is a styrene-butadiene copolymeravailable under the trade designation PLIOLITE from Goodyear Chemical(Akron, Ohio). Yet another suitable polymer is a phenoxy resin availableunder the trade designation INCHEMREZ PKHM-301 from InChem. Corp. (RockHill, S.C.).

A styrene/allyl alcohol copolymer may also be suitably included in thecoating. A commercially available styrene/allyl alcohol copolymer isSAA-100 from Lyondell Chemical Company (Houston, Tex.).

Mixtures of polymers may also be suitably employed as the binder. Forexample, a mixture of BUTVAR B-76 and SAA-100 in a ratio of about2:1-20:1 by weight is suitable.

The materials described above are given only as non-limiting examples.Other suitable polymers will be appreciated by those skilled in the art.

The coating on the receptor sheet may be optionally textured with atexturizing material so as to present a surface having a controlleddegree of roughness. The texturizing material may be, for example, aninert particulate material such as polymeric beads, silica particles,etc.

The presence of some surface roughness is found to be advantageous whena receptor sheet is brought into proximity with a film for imaging.Protrusions in the receptor sheet regulate precisely the relationshipbetween the film and the receptor element, and provide a generallyuniform gap between the donor element and the receptor element duringimaging. The magnitude of the protrusions on the receptor sheet, whetherformed by beads or particulate matter or by texturing, may be measuredusing known techniques such as interferometry or by examination of thesurface using an optical or electron microscope.

As mentioned above, the texturizing material may be an inert particulatematerial such as, for example, polymeric beads, silica particles, metaloxide particles, inorganic salts, etc. The shape of the beads ispreferably spherical, oblong, ovoid, or elliptical. The texturizingmaterial may be of essentially uniform size (i.e., monodisperse), or mayvary in size. Dispersions of inorganic particles such as silicagenerally have a range of particle sizes, whereas monodispersesuspensions of polymer beads are readily available. Whichever type ofpopulation is used, the particles should not project above the plane ofthe surface of the receptor element by more than about 8 μm on average,but should preferably project above said plane by at least about 1 μm,and more preferably at least about 3 μm. In some constructions, it isadvantageous to add two distinct sets of beads with different averagesizes. This allows the flexibility to balance haze with slip orseparation characteristics.

Nonlimiting examples of polymeric beads that may be suitable includepoly(methyl methacrylate) and poly(stearyl methacrylate) beads, andbeads comprising diol dimethacrylate homopolymers or copolymers.Suitable polymeric beads also include those made from polystyrene,phenol resins, melamine resins, epoxy resins, silicone resins,polyethylene, polypropylene, polyesters, polyimides, etc.

In general, the polymeric beads should have a particle size ranging fromabout 3-50 μm, preferably from about 5-25 μm. The coverage of the spacerbeads in the coating may range from about 5-2,000 beads/mm². As theparticle size of the beads increases, then proportionally fewer beadsare required.

By way of example, one suitable texturizing material includesmonodisperse beads of poly(methyl methacrylate) having an averagediameter of approximately 10 μm. Such beads are commercially available.

The concentration of texturizing material in the coating on the receptorsheet should be sufficient to provide an areal density of about 100-500particles/mm². By way of example, a suitable particle areal density isabout 200 particles/mm². In one embodiment, the coating on the receptorsheet comprises about 20-80 parts binder to about 1 part texturizingmaterial, by weight.

As an alternative to the use of beads or particles the receptor elementsurface may be physically textured to provide the required protrusions.Metal surfaces, such as aluminum, may be textured by graining andanodizing. Other textured surfaces may be obtained by microreplicationtechniques, as are known in the art.

Forming a Mask Image

In the practice of the invention, a mask image is formed on either acarrier sheet or a receptor sheet. The step of forming a mask imagegenerally includes producing exposed areas and unexposed areas of theimageable material. The choice of imaging mechanism will determine thepossible variations in forming the mask image, as discussed below.

The methods include the step of producing exposed and non-exposed areasof the imageable material. In this step, the imageable material may beexposed to imaging radiation in selected areas, otherwise known as“imagewise exposure.”

Methods of imagewise exposing the film are conventional in the art. Bothanalog and digital methods of imagewise exposing the film are suitable.Digital methods are preferred by many users due to the ease of imagingand the increased availability of digital imaging apparatus.

In some embodiments of the invention, imagewise exposure is efficientlyaccomplished using laser radiation from a laser that is scanned orrasterized under computer control. Any of the known scanning devices maybe used, e.g., flat-bed scanners, external drum scanners, or internaldrum scanners. In these devices, the film to be imaged is secured to thedrum or bed, and the laser beam is focused to a spot that can impinge onthe imageable material. The laser spot is scanned over the area to beimaged while the laser output is modulated in accordance withelectronically stored image information (i.e., digital data). Two ormore lasers may scan different areas of the imageable materialsimultaneously, to increase throughput. This embodiment is illustratedin FIGS. 1A and 3A. In FIG. 1A, infrared radiation 2 is used to producea mask image 4 on a carrier sheet 6. Similarly, FIG. 3A illustratesinfrared radiation 22 used to form a mask image 24 on a carrier sheet26.

In certain embodiments a portion of the imageable material is imagewiseexposed to infrared radiation. The infrared radiation may be, forexample, in the range of about 750 nm to about 1200 nm. In the practiceof this embodiment, suitable imageable materials include a componentthat is sensitive to infrared radiation, as described above. Thiscomponent may, for example, convert infrared radiation to heat. Thegeneration of heat in the imageable material may then result in aphysical or chemical change in another component of the imageablematerial. In this embodiment, the film may be suitably mounted to aninfrared imager and exposed imagewise to infrared radiation. Infraredradiation may be provided, for example, by an infrared laser such as adiode laser (e.g., ˜830 nm) or a Nd:YAG laser (˜1064 nm), which may bescanned or rasterized under computer control.

Suitable infrared imagers include those infrared imagers used inproofing processes. Examples of such infrared imagers include DESERTCAT88, available from ECRM (Tewksbury, Mass.). Infrared imagers for CTPlithographic plate applications, such as TRENDSETTER from Creo (Burnaby,British Columbia) and DIMENSION from Presstek (Hudson, N.H.) may also beused. Imagers configured for imaging flexographic articles, such asCYREL Digital Imager (CDI SPARK) manufactured by Esko-Graphics(Kennesaw, Ga.), ThermoFlex by Creo (Burnaby, British Columbia), andOMNISETTER from Misomex International (Hudson, N.H.) could also beemployed.

In other embodiments, the imageable material is exposed to visible laserlight. The visible light may be, for example, in the range of about400-750 nm. Commercially available filmsetters and imagesetters can beused. For example ACCUSET Plus (visible red laser diode, 670 nm) fromAgfa-Gevaert (Belgium), ADVANTAGE DL3850 (410 nm) from Agfa-Gevaert,LUXEL V-9600 (410 nm) from Fuji Photo Film, DIAMONDSETTER(frequency-doubled Nd:YAG laser; 532 nm) from Western Lithotech (St.Louis, Mo.), SELECTSET 5000 (HeNe, 630 nm) from Agfa-Gevaert.

In still other embodiments, the imageable material is exposed toultraviolet radiation, by laser direct imaging (LDI). The ultravioletradiation may be in the range of about 150-410 nm. DP-100 from Orbotech(Billerica, Mass.), and DIGIRITE 2000 from Etec Systems (Tucson, Ariz.)may be suitable for UV laser imaging.

In the practice of some embodiments of the invention, a mask image isformed on the carrier sheet by producing exposed and non-exposed areasof the imageable material. The step of forming the mask image may alsocomprise a step of removing either exposed areas or unexposed areas ofthe imageable material from the film. In certain embodiments, theexposed areas are removed from the carrier sheet, leaving a mask imageon the carrier sheet.

For these embodiments, a receptor sheet may optionally be used forremoving waste imageable material. The receptor sheet may be anymaterial suitable for removing the waste imageable material such as, forexample, papers, transparent films, and metal sheets. One or morecoatings may be applied to the receptor sheet before radiation of thefilm to facilitate transfer of the imageable material to the receptor.After imaging, the receptor sheet may be removed from the film to revealthe mask image on the carrier sheet. A complementary image to the maskimage may remain on the receptor sheet.

In other embodiments, a mask image is formed on the carrier sheet byproducing exposed and non-exposed areas of the imageable material, andremoving unexposed areas from the carrier sheet.

In some embodiments, the mask image residing on the carrier sheet mayoptionally be cured by subjecting it to heat treatment, provided thattransfer property of the mask image is not adversely affected. Heattreatment may be done by a variety of means, such as storage in an oven,hot air treatment, contact with a heated platen or passage through aheated roller device. In other embodiments, heat treatment is notnecessary for curing to take place.

In still other embodiments, a mask image is formed on a receptor sheetby producing exposed and non-exposed areas of the imageable material,causing exposed areas to be transferred to the receptor sheet. In theseembodiments, the carrier sheet is subsequently removed from the maskimage, before the mask image is transferred to the photosensitivematerial. The film may be provided with a receptor sheet in contact withthe imageable material, or alternatively the imageable material iscontacted with a separate receptor sheet.

Suitable receptor sheets are described above. The characteristics ofsuitable receptor coatings may depend on the type of removal systemused. For example, to promote transfer in a melt-stick system, it may besuitable to employ similar or identical binders for both the receptorcoating and the binder of the imageable material. In a particularembodiment, polyvinyl butyral such as BUTVAR B-76 available fromSolutia, Inc. (St. Louis, Mo.), or a similar binder is coated on to thereceptor before the receptor is placed in contact with the imageablematerial.

Where a separate receptor sheet is used during imaging, the film and thereceptor sheet are assembled in close proximity prior to imaging, withthe image-receiving side of the receptor sheet adjacent to the imageablematerial. The phrase “close proximity” in this context can mean that theimageable material and receptor sheet are brought into contact, or thatthey do not contact each other but are sufficiently close to allowtransfer of imageable material or colorant upon exposure to imagingradiation. Vacuum hold-down or a mechanical means may be used to securethe film and receptor sheet in assembly.

Next, the assembly of the donor and receptor sheets is imagewise exposedusing imaging radiation to form a mask image, as described below.Imagewise exposure to imaging radiation causes imagewise transfer ofimageable material or colorant from the film to the receptor sheet.After imaging, the film may be removed from the receptor sheet to revealthe mask image on the receptor sheet.

In some embodiments, the mask image residing on the receptor sheet mayoptionally be cured by subjecting it to heat treatment, provided thattransfer property of the mask image is not adversely affected. Heattreatment may be done by a variety of means, such as storage in an oven,hot air treatment, contact with a heated platen or passage through aheated roller device. In other embodiments, heat treatment is notnecessary for curing to take place.

Each of the foregoing variations will be discussed in detail below, inrelation to several imaging mechanisms. The listed imaging mechanismsshould be considered as non-limiting examples only, as the methods canbe readily adapted to work with other imaging mechanisms.

Ablation

In one embodiment, the exposed areas of the imageable material areremoved through ablation. In this embodiment, the exposed imageablematerial is propelled from the carrier sheet by generation of a gas.Specific binders that decompose upon exposure to heat (such as laserradiation) to rapidly generate a gas may be used in the imageablematerial. The build-up of gas under or within the exposed areas of theimageable material creates pressure that propels the imageable materialoff of the carrier sheet in the exposed areas. This action isdistinguishable from other mass transfer techniques in that a chemicalchange (e.g., bond-breaking), rather than a physical change (e.g.,melting, evaporation or sublimation), causes an almost complete transferof the imageable material rather than a partial transfer.

In one ablative mode of imaging by the action of a laser beam, a filmhaving a layer of imageable material comprising a colorant, aninfrared-absorbing material, and a binder is imaged. Energy provided bythe laser drives off the imageable material at the spot where the laserbeam hits the element.

In one suitable embodiment, the binder serves as a “heat-combustible”material as described above, and as further discussed in U.S. Pat. No.6,521,390 to Leinenbach, et al. The heat-combustible binder mayoptionally be present in a barrier layer for the practice of thisembodiment.

For an ablative imaging mechanism, any colorant can be used provided itcan be ablated by the action of the laser. Suitable dyes for use as thecolorant are described, for example, in U.S. Pat. No. 5,576,144 toPearce, et al. and references cited therein.

By an ablative mechanism, a mask image may be generated on a carriersheet using a suitable film. A debris collector, such as, for example, avacuum or a suitable receptor sheet, may be placed near imageablematerial to retrieve the exposed imageable material after it ispropelled from the carrier sheet.

A mask image may also be generated on a suitable receptor sheet by anablative mechanism. Ablation transfer is reported, for example, in U.S.Pat. No. 5,171,650 to Ellis, et al. and in International Publication WO90/12342.

Melt-Stick Transfer

In still another embodiment, the exposed areas of the imageable materialare removed through melt-stick. In a melt-stick system, the imageablematerial transfers in a molten or semi-molten state from the carriersheet to a suitable receptor sheet upon exposure to radiation. Themolten or semi-molten state is characterized by reduced viscosity, whichprovides flowability to the imageable material. The imageable materialflows across to, and adheres to the surface of the receptor sheet withgreater strength than it adheres to the carrier sheet. Physical transferof the imageable material from the carrier sheet to the receptor sheetin exposed areas thus results. Following transfer, the carrier sheet,along with untransferred imageable material, is separated from thereceptor sheet.

In one embodiment, the mask image comprises the unexposed areasremaining on the carrier sheet. In the practice of this embodiment, thereceptor sheet and the transferred imageable material are generally (butnot necessarily) discarded as waste.

In another embodiment, the mask image comprises the exposed areas of theimageable material that are transferred to the receptor sheet. In thepractice of this embodiment, the carrier sheet and remaining imageablematerial are generally discarded as waste.

Further aspects and requirements for melt-stick transfer may be found inU.S. Pat. No. 5,819,661 to Lewis, et al. and in U.S. Pat. No. 5,238,778to Hirai, et al., each of which is incorporated by reference herein.

Laser-Induced Film Transfer

In still another embodiment, the exposed areas of the imageable materialare removed from the carrier sheet through laser-induced film transfer(“LIFT”). In a LIFT system, a release layer containing a latentcrosslinking agent is disposed between the carrier sheet and imageablematerial. The crosslinking agent reacts with the binder to form a highmolecular weight network in the exposed areas. The effect of thiscrosslinking is better control of melt flow phenomena, transfer of morecohesive material to the receptor, and higher quality edge sharpness ofthe mask image. Examples of this type of system may be found in U.S.Pat. No. 5,935,758 to Patel, et al. which is incorporated herein byreference in its entirety.

In one embodiment, the imageable material includes a transferablecolorant and an infrared-absorbing dye. The colorant is capable of beingtransferred upon exposure to infrared radiation to a suitable receptorsheet. In another embodiment, the imageable material comprises a binderincluding a hydroxylic polymer, a transferable colorant, a fluorocarbonadditive, a cationic infrared-absorbing dye, and a latent crosslinkingagent, which are described above.

In one embodiment, the mask image comprises the unexposed areasremaining on the carrier sheet. In the practice of this embodiment, thereceptor sheet and the transferred imageable material are generally (butnot necessarily) discarded as waste.

In another embodiment, the mask image comprises the exposed areas of theimageable material that are transferred to the receptor sheet. In thepractice of this embodiment, the carrier sheet and remaining imageablematerial are generally discarded as waste.

Peel-Apart

In yet another embodiment, the exposed areas of the imageable materialare removed from the carrier sheet using a suitable receptor sheet in aso-called “peel-apart” system. A peel-apart mechanism depends on theability to generate differential adhesion properties in the imageablematerial. After imagewise exposure of the film, the receptor sheet isseparated from the carrier sheet, and either exposed or unexposed areasof the imageable material remain on the carrier sheet.

U.S. Pat. No. 6,013,409 to Chou (incorporated by reference herein in itsentirety) describes a suitable peel-apart imaging system. One elementuseable for peel-apart imaging includes a carrier sheet, a“photohardenable layer” comprising colorant, a “photopolymeric adhesive”layer, and an optional release layer.

Other suitable constructions for peel-apart imaging are described inreferences cited at col. 3, line 25 to col. 4, line 16 of U.S. Pat. No.6,013,409 to Chou, for example.

In one embodiment, the mask image comprises the imageable materialremaining on the carrier sheet. In the practice of this embodiment, thereceptor sheet and the transferred imageable material are generally (butnot necessarily) discarded as waste.

In another embodiment, the mask image comprises the imageable materialthat is transferred to the receptor sheet. In the practice of thisembodiment, the carrier sheet and remaining imageable material aregenerally discarded as waste.

Dye Sublimation or Diffusion

In another embodiment, colorant from the exposed areas of the imageablematerial is removed through sublimation. Sublimation techniques involvea mechanism wherein the colorant included in the imageable material aresublimed or diffused without simultaneous transfer of the binder. In dyesublimation, a sublimable colorant is converted into gaseous form anddissipated into the atmosphere, or optionally directed towards asuitable receptor sheet.

Dye sublimation is reported, for example, in U.S. Pat. No. 5,126,760 toDeBoer, and U.S. Pat. No. 5,994,026 to DeBoer, et al., each of which isincorporated by reference in its entirety. Thermal dye diffusiontransfer as described, for example, in U.S. Pat. No. 5,330,962 to DeBraabandere, et al. is also suitable as an imaging method.

Sublimable colorants that can be used include dyes described, forexample, in U.S. Pat. Nos. 5,576,141, 5,576,142, 5,521,050, 5,521,051,and 5,510,228, to Neumann, et al. Generally, such dyes are present inthe imageable material in an amount of at least about 25 wt %.

By a dye sublimation mechanism, a mask image may be generated on acarrier sheet using a suitable film, and without the need for a receptorsheet.

In another embodiment, a receptor sheet is employed to capture thesublimed colorant. The mask image comprises the imageable materialremaining on the carrier sheet. In the practice of this embodiment, thereceptor sheet and the transferred colorant are generally (but notnecessarily) discarded as waste.

In another embodiment, the mask image comprises the colorant that istransferred to a receptor sheet. In the practice of this embodiment, thecarrier sheet and remaining imageable material are generally discardedas waste.

Conventional Development

In still another embodiment, the exposed areas of the imageable materialare removed by development. In this embodiment, the film is washed witha suitable developer to remove the exposed areas of the imageablematerial, while unexposed areas remain on the carrier sheet. Theimageable material in this embodiment is a positive-working imageablecomposition comprising the colorant. Positive-working imageablecompositions are well-known in the art. Imagewise exposure of apositive-working composition causes exposed areas to become more solublein a suitable developer solution.

Suitable developers for these positive-working imaging compositions areaqueous developers having a pH in the range of about 9 to about 14.Conventional developers comprising water, tetra-alkyl ammoniumhydroxide, and surfactants, for example, are suitable.

In other embodiments, the non-exposed areas of the imageable materialare removed from the carrier sheet to produce the mask image. Theimageable material in this embodiment is a negative-working imageablecomposition comprising the colorant. Negative-working imageablecompositions are well-known in the art. Imagewise exposure of anegative-working composition causes exposed areas to become insoluble ina developer solution, while unexposed areas remain soluble. By way ofexample, imagewise exposure may cause photopolymerization of imageablematerial in exposed areas.

In these embodiments, the non-exposed areas may be removed bydevelopment, for example. The film is washed with a suitable developerto remove the unexposed areas of the imageable material, while exposedareas remain on the carrier sheet. Suitable developers fornegative-working systems are aqueous-based or solvent-based developingcompositions. Aqueous developers typically have pH in the range of about7 to about 13, and may comprise additives, such as water-misciblehigh-boiling organic solvents, surfactants, dispersants, etc.

Developers for both positive-working and negative-working compositionsare commercially available from a variety of sources.

Silver Halide Emulsion

As another suitable imaging method, a mechanism that causes a physicalor chemical change in the imageable material that changes the degree ofopacity or transparency of the imageable material to curing radiationmay be employed. One such imaging method incorporates a silver halideemulsion as the imageable material, for example.

Imaging methods using silver halide and dry silver halide, particularlylaser addressable photothermographic silver halide with dry processing,are also suitable. U.S. Pat. No. 6,713,241 to Vaeth, et al. (which isincorporated by reference herein in its entirety) and references thereindescribes dry thermographic silver halide imaging.

Transferring the Mask Image to Photosensitive Material

In another step of the invention, the mask image is transferred to aphotosensitive material that is sensitive to a curing radiation. In oneembodiment, the mask image includes the exposed areas of the imageablematerial. In another embodiment, the mask image includes the non-exposedareas of the imageable material. The photosensitive material ishardenable or curable by exposure to the curing radiation. Thephotosensitive material generally includes a polymer or prepolymer, andmay be hardened or cured by polymerization or crosslinking upon exposureto the curing radiation. The photosensitive material is generally,although not necessarily, disposed on a substrate.

The result of one embodiment of this step is illustrated in FIGS. 1B and3B. In FIG. 1B the mask image 4 disposed on the carrier sheet 6 is showntransferred onto a separation layer 8 that is disposed on aphotosensitive material 10. In this illustrated embodiment, thephotosensitive material 10 is disposed on a substrate 12. Similarly, inFIG. 3B, the mask image 24 disposed on the carrier sheet 26 is showntransferred onto a separation layer 28 that is disposed on top of aphotosensitive material 30. In this illustrated embodiment, thephotosensitive material 30 is disposed on a substrate 32.

Photosensitive Materials

Another component used in the method of the present invention is animageable article that is able to produce a relief image. Examples ofimageable articles include a flexographic printing plate, a printedcircuit board (“PCB”), and a lithographic printing plate.

The imageable article includes at least a photosensitive material. Theimageable article may also include a suitable substrate. Furthermore,optional components, such as a separation layer, a cover sheet, or ametal layer may be included in the imageable article. The photosensitivematerial may either be positive working or negative working. A negativeworking photosensitive material is hardenable or curable by exposure toa curing radiation. The photosensitive material generally includes apolymer or prepolymer, and may be hardened or cured by polymerization orcrosslinking upon exposure to the curing radiation.

In some embodiments, the photosensitive material is anultraviolet-curable resin. In particular embodiments, theultraviolet-curable resin is disposed on a substrate and is protected bya removable cover sheet. Ideally the substrate is made from adimensionally stable material, such as polyester film or an aluminumsheet.

A separation layer that protects the ultraviolet-curable resin fromfingerprinting or other damage may be disposed between the ultravioletcurable resin and the cover sheet. This layer is sometimes referred toin the art as an anti-tack layer, release layer, slip layer, orprotective layer. For the purposes of the present specification, theseparation layer is considered to be part of the photosensitivematerial. The separation layer may include polyamide, such as forexample, MACROMELT 6900, available from Henkel Corporation (Gulph Mills,Pa.), polyvinyl alcohol, copolymers of ethylene and vinyl acetate,amphoteric interpolymers, cellulosic polymers, such as hydroxyalkylcellulose, and cellulose acetate butyrate, polybutyral, cyclic rubbers,and combinations thereof. Amphoteric interpolymers are described in U.S.Pat. No. 4,293,635 to Flint, et al. which is hereby incorporated byreference.

The ultraviolet-curable resin may also include an elastomeric binder, atleast one monomer and an initiator, where the initiator has asensitivity to non-infrared actinic radiation. In most cases, theinitiator will be sensitive to ultraviolet or visible radiation or both.Examples of suitable initiator compositions have been reported in U.S.Pat. No. 4,323,637 to Chen, et al., U.S. Pat. No. 4,427,749 toGruetzmacher, et al., and U.S. Pat. No. 4,894,315 to Feinberg, et al.

The elastomeric binder may be a single polymer or mixture of polymerswhich may be soluble, swellable or dispersible in aqueous, semi-aqueousor organic solvent developers. Suitable binders include those describedin, U.S. Pat. No. 3,458,311 to Alles, U.S. Pat. No. 4,442,302 to Pohl,U.S. Pat. No. 4,361,640 to Pine, U.S. Pat. No. 3,794,494 to Inoue, etal., U.S. Pat. No. 4,177,074 to Proskow, U.S. Pat. No. 4,431,723 toProskow, and U.S. Pat. No. 4,517,279 to Worns. Binders which aresoluble, swellable or dispersible in organic solvent developers includenatural or synthetic polymers of conjugated diolefin hydrocarbons,including polyisoprene, 1,2-polybutadiene, 1,4-polybutadiene,butadiene/acrylonitrile, butadiene/styrene thermoplastic-elastomericblock copolymers and other copolymers. The block copolymers discussed inU.S. Pat. No. 4,323,636 to Chen, U.S. Pat. No. 4,430,417 to Heinz, etal., and U.S. Pat. No. 4,045,231 to Toda, et al. may be used. The bindermay comprise at least about 65% by weight of the ultraviolet-curableresin. The term binder, as used herein, encompasses core-shell microgelsand blends of microgels and preformed macromolecular polymers, such asthose described in U.S. Pat. No. 4,956,252 to Fryd, et al.

The ultraviolet-curable resin may also contain a single monomer ormixture of monomers which must be compatible with the binder to theextent that a clear, non-cloudy photosensitive layer is produced.Monomers that may be used in the ultraviolet-curable resin are wellknown in the art and include, but are not limited to,addition-polymerization ethylenically unsaturated compounds havingrelatively low molecular weights (generally less than about 30,000 Da).Suitable monomers have a relatively low molecular weight, less thanabout 5000 Da. Unless described otherwise, throughout the specificationmolecular weight is the weight-average molecular weight. Examples ofsuitable monomers include, but are not limited to, t-butyl acrylate,lauryl acrylate, the acrylate and methacrylate mono- and poly-esters ofalcohols and polyols such as alkanols, e.g., 1,4-butanediol diacrylate,2,2,4-trimethyl-1,3 pentanediol dimethacrylate, and2,2-dimethylolpropane diacrylate, alkylene glycols, e.g., tripropyleneglycol diacrylate, butylene glycol dimethacrylate, hexamethylene glycoldiacrylate, and hexamethylene glycol dimethacrylate, trimethylolpropane, ethoxylated trimethylol propane, pentaerythritol, e.g.,pentaerythritol triacrylate, dipentaerythritol, and the like. Otherexamples of suitable monomers include acrylate and methacrylatederivatives of isocyanates, esters, epoxides and the like, such asdecamethylene glycol diacrylate, 2,2-di(p-hydroxyphenyl)propanediacrylate, 2,2-di (p-hydroxyphenyl)propane dimethacrylate,polyoxyethyl-2,2-di(p-hydroxyphenyl)propane dimethacrylate, and 1-phenylethylene-1,2-dimethacrylate. Further examples of monomers can be foundin, U.S. Pat. No. 4,323,636 to Chen, U.S. Pat. No. 4,753,865 to Fryd, etal., U.S. Pat. No. 4,726,877 to Fryd, et al., and U.S. Pat. No.4,894,315 to Feinberg, et al. The monomer may comprise at least 5% byweight of the ultraviolet-curable resin.

The photoinitiator may be any single compound or combination ofcompounds which is sensitive to ultraviolet radiation, generating freeradicals which initiate the polymerization of the monomer or monomerswithout excessive termination. The photoinitiator should be sensitive tovisible or ultraviolet radiation. The photoinitiator may also beinsensitive to infrared and/or visible radiation and should be thermallyinactive at and below 185° C. Examples of suitable photoinitiatorsinclude the substituted and unsubstituted polynuclear quinones. Examplesof suitable systems have been disclosed in, U.S. Pat. No. 4,460,675 toGruetzmacher and U.S. Pat. No. 4,894,315 to Feinberg, et al.Photoinitiators are generally present in amounts from 0.001% to 10.0%based on the weight of the ultraviolet-curable resin.

The ultraviolet-curable resin may contain other additives depending onthe final properties desired. Such additives include sensitizers,plasticizers, rheology modifiers, thermal polymerization inhibitors,tackifiers, colorants, antioxidants, antiozonants, or fillers.Plasticizers may be used to adjust the film-forming properties of theelastomer. Examples of suitable plasticizers include aliphatichydrocarbon oils, e.g., naphthenic and paraffinic oils, liquidpolydienes, e.g., liquid polybutadiene, liquid polyisoprene. Generally,plasticizers are liquids having molecular weights of less than about5,000 Da, but can have molecular weights up to about 30,000 Da.Plasticizers having low molecular weight will encompass molecularweights less than about 30,000 Da.

The thickness of the ultraviolet-curable resin may vary depending uponthe type of printing plate desired. In one embodiment, theultraviolet-curable resin may be, for example, from about 20-250 mils(500-6400 microns) or greater in thickness, more particularly from about20-100 mils (500-2500 microns) in thickness.

In one embodiment, the imageable article is a flexographic printingplate precursor that includes a suitable ultraviolet-curable resin. Thematerials that are used to make flexographic printing plates typicallyinclude a substrate, and one or more photosensitive layers comprising aphotosensitive material that includes a polymer or prepolymer. Examplesof commercially available flexographic printing plates that may be usedin the present invention include, for example, FLEXCEL, available fromKodak Polychrome Graphics (Norwalk, Conn.), CYREL Flexographic plate,available from DuPont (Wilmington, Del.), NYLOFLEX FAR 284, availablefrom BASF, FLEXILIGHT CBU available from Polyfibron, and ASAHI AFP XDI.

Photosensitive material may also be used with a mask image to form aprinted circuit board (“PCB”). In a PCB, a conducting layer (alsoreferred to as a printed circuit) is formed on a substrate in thepattern dictated by the mask image. The printed circuit may then directelectrical voltages and currents between various electrical components,such as resistors, capacitors, integrated circuits and other electronicdevices. The electrical components are soldered onto the printed circuitat a stage after the formation of the printed circuit.

Suitable PCB precursors may contain a substrate, a metal layer and aphotosensitive material. The substrate may be polyimide film,glass-filled epoxy or phenol-formaldehyde or any other insulatingmaterials known and used in the industry, and of any thickness deemednecessary.

The metal layer covering the substrate may include a conductive metal.One suitable example is copper, although any other suitable metal oralloy of metals may be used.

The photosensitive material may include an ultraviolet-curable resin.One example of a suitable ultraviolet-curable resin for use on a PCBprecursor includes oligomers and monomers, photoinitiators, and abinder.

Suitable oligomers and monomers include those that may be cross-linked,in the presence of a photoinitiator, upon exposure to ultravioletradiation. The oligomers and monomers may include those described above.These components may comprise between 35% and 75% by weight of theultraviolet-curable resin.

Photoinitiators should be capable of generating and promoting freeradicals that will assist in cross-linking the oligomers and monomersupon exposure to ultraviolet radiation. Suitable photoinitiators aredescribed above. The photoinitiator may comprise up to about 10% of theweight of the oligomers and monomers included in the ultraviolet-curableradiation.

The binder should be soluble in water or dilute alkali developers andwell as organic developers. The binder should also be soluble in etchingagents, such as aqueous ferric chloride solution. Examples of suitablebinders include, for example, novolaks (functionally substitutedphenol-formaldehyde resins), styrene maleic anhydride copolymers,polyvinyl methyl ether/maleic anhydride copolymer and its esters,hydroxy propyl cellulose and esterified rosin-maleic esters.

Other components, such as fillers and wetting agents, as well as dyes orpigments to aid visual examination may also be included in theultraviolet-curable resin used in forming a PCB precursor.

The coating thickness of the ultraviolet-curable resin in the PCBprecursor may be between 3 microns and 30 microns, more particularly 12microns, in order to obtain maximal difference in solubility betweencured and uncured regions and optimal adhesion properties.

The photosensitive material used in the PCB precursor construction mayalso be positive working, meaning that the photosensitive materialbecomes more developable upon exposure to ultraviolet or visibleradiation. In these PCB precursors, the areas of the photosensitivematerial that are not exposed to radiation will remain on the PCBprecursor after developing and are known in the art.

Methods of Transfer

The step of transferring the mask image includes placing the mask imageand the accompanying carrier sheet or receptor sheet (the “sheet”) onthe photosensitive material, with the mask image in proximity with thephotosensitive material. If the photosensitive material is disposedbetween a substrate and a cover sheet, the cover sheet or the substrateshould be removed before placing the mask image in proximity to thephotosensitive material. If a separation layer is included on thephotosensitive material, the mask image may optionally be transferred sothat the separation layer remains between the mask image and thephotosensitive material.

In one embodiment, the step of transferring the mask image may includelaminating the mask image to the photosensitive material. The mask imageis contacted to the photosensitive material to form an assembly, andthen the mask image is laminated to the photosensitive material. In someembodiments, lamination of the mask image to the photosensitive materialmay be accomplished by applying pressure to the assembly. In otherembodiments, the mask image may be laminated to the photosensitivematerial by application of heat. Laminating may also include applyingboth pressure and heat to the assembly.

Commercially available laminators which provide both heat and pressureto the assembly may be used. Suitable laminators include, for exampleKODAK model 800XL APPROVAL LAMINATOR, available from Eastman Kodak Co.(Rochester, N.Y.), CODOR LPP650 LAMINATOR from CODOR laminating system,(Amsterdam, Holland), and LEDCO HD laminators, available from Filmsource(Casselbury, Fla.). These laminators provide adequate heat and pressureto laminate the mask image to the photosensitive material. One method oflaminating the mask image to the photosensitive material is to place asheet of unexposed photosensitive material disposed on a substrate onthe entrance tray of the laminator. A protective cover sheet, ifpresent, is removed from the photosensitive material. The mask image andaccompanying sheet is placed on the photosensitive material, with themask image in proximity with the photosensitive material to form anassembly. The assembly is fed into the laminator at the desired speed,temperature and pressure. After exiting the laminator, the laminatedassembly of plate and mask is allowed to cool to room temperature andthe sheet on the mask is peeled away from the laminated assembly.

By way of example only, a 67 mil (1.7 mm) FLEXCEL SRH photopolymerflexographic printing plate, available from Kodak Polychrome Graphics(Norwalk, Conn.), may be laminated to a mask image using the KODAK model800XL APPROVAL LAMINATOR by removing the protective cover sheet from theplate and positioning the mask image face down on the anti-tack surfaceof the plate. A 50-mil paperboard stock, cut slightly longer and widerthat the plate, may be placed under the assembly. The assembly may thenbe fed into the laminator entrance and laminated with a surfaceinterface temperature of about 230° F. (110° C.) and a pressure of about15 pounds per square inch (1 kg/cm²). The laminator speed may be set at,for example, 30 inches/minute (76.2 cm/minute) resulting in a thermaldwell time of 48 seconds. Upon exiting the laminator the assembly may beair cooled for 3 minutes.

In another embodiment, the step of transferring may include selectiveadhesion of the mask image to the photosensitive material. In thisembodiment, the mask image is contacted to the photosensitive material,and the mask image readily adheres to the photosensitive material,facilitating easy removal of the sheet.

In still another embodiment, the step of transferring the mask image mayutilize pressure-sensitive adhesion. In this embodiment, the mask imageis contacted to the photosensitive material, and under the influence ofpressure the mask image becomes more adhesive to the photosensitivematerial than to the carrier sheet. A pressure-sensitive adhesive may beincorporated into the photosensitive material, the separation layer, orthe imageable material. The pressure-sensitive adhesive may also beplaced in a separate layer between the imageable material and thephotosensitive material. The pressure-sensitive adhesive may include acopolymer of monomers, a first monomer being an acrylic acid ester ofnon-tertiary alkyl alcohol and at least one second monomercopolymerizable with the acrylic acid ester. The second monomer may be,for example, acrylic acid, methacrylic acid, itaconic acid, acrylamide,methacrylamide, acrylonitrile, or methacrylonitrile and may constitute 3wt %-12 wt % of the total of the monomers. One example of a suitablepressure-sensitive adhesive may be found in U.S. Pat. No. Re. 24,906 toUlrich.

In embodiments using adhesion as the method of transfer, the adhesivematerials used should be selected in view of the components in the maskimage and the components in the photosensitive material. Suitableadhesives should generally be transparent to and not scatter theradiation used to cure the photosensitive material. For example, anadhesive that scatters the radiation would not be suitable because itwould distort the ability of the mask image to create cured andnon-cured areas of the photosensitive material and reduce the resolutionof the relief image.

In some embodiments, at least portions of a release layer aretransferred along with the mask image to provide a desired oxygenpermeability, as discussed above. At least the portions of the releaselayer corresponding to the transferred mask image are transferred. Inother embodiments, the release layer may be transferred intact (i.e.,contiguous). The transferred release layer can originate from the film,or from a receptor sheet.

Removing the Carrier Sheet or Receptor Sheet from the Mask Image

Another step of the inventive method involves removing the carrier sheetor receptor sheet (the “sheet”) from the mask image on the imagedarticle. In one embodiment, the sheet is removed before exposing thephotosensitive material to curing radiation. This embodiment isillustrated in FIGS. 1C and 1D. In FIG. 1C, the carrier sheet 6 is shownremoved from the mask image 4 and the mask image 4 is left on theseparation layer 8 before the photosensitive material 10 is exposed to acuring radiation 14. In the embodiment illustrated in FIG. 1D, thephotosensitive material 10 is exposed to the curing radiation 14 afterthe carrier sheet 6 is removed from the mask image 4.

Unlike the analog methods of imaging wherein a transparent, orsemi-transparent sheet remains during the curing of the photosensitivematerial, the method of the present invention may provide enhancedresolution for the resulting relief image for at least two reasons.First, removal of the sheet may reduce scattering of radiation duringthe curing of the photosensitive material. Second, since a vacuum is notrequired when the mask image is transferred to the photosensitivematerial, the matting agents, or beads, typically contained in theimageable material used in analog methods for better vacuum draw-downare not required thus avoiding the additional light scattering thatsometimes results from these matting agents.

In another embodiment, the sheet is removed after exposing thephotosensitive material to curing radiation. Even if the sheet is lefton the mask image during exposure to the curing radiation, the methoddiffers from the known analog method because vacuum draw-down of maskimage is not required. This embodiment is illustrated in FIGS. 3C and3D. As illustrated in FIG. 3C, a carrier sheet 26 remains on the maskimage 24 while the photosensitive material 30 is exposed to the curingradiation 34. Following exposure to the curing radiation 34, the carriersheet 26 is removed from the mask image 24, the result of which isillustrated in FIG. 3D.

The sheet may be separated from the mask by peeling the sheet away fromthe mask image, for example. Separating the sheet may be done manually,or it may be done mechanically. Preferably, the force required to peelthe carrier sheet from the mask image is less than about 15 gm/inch,more particularly about 2.5-6 gm/inch, and eve more particularly 5gm/inch. As described above, one embodiment of film used to form themask image of the present invention employs a film that includes arelease layer and an imageable material that includes a thermallyadhesive binder. In this particular embodiment, the force required topeel the carrier sheet from the mask image of utilizing this particularfilm has been found to be about 5 gm/inch.

In another embodiment, the sheet is separated from the mask image bydissolving or dispersing the sheet in a suitable solvent. The solventused in this embodiment will depend upon the type of sheetphotosensitive composition and upon the mask image.

In yet another embodiment, contacting the carrier sheet with a suitablesolvent may enable the carrier sheet to be released from the mask image,such as by causing adhesion failure between the carrier sheet and themask image.

In some embodiments, a release layer is disposed between the imageablematerial and the sheet from which the mask image is transferred. Therelease layer may facilitate separation of the sheet from the maskimage, enhanced resolution and better cure for longer run length and inkreceptivity. However, a release layer is not required for performance ofthis step.

Exposing the Photosensitive Material Through the Mask Image

Another step of the invention includes exposing the photosensitivematerial to curing radiation through the mask image to form an imagedarticle. In this step, the curing radiation is projected onto thephotosensitive material through the mask image, so that some of theradiation is preferentially blocked by the mask image. In unmaskedareas, curing radiation will impinge upon the photosensitive material tocause hardening or curing. The mask image should therefore besubstantially opaque to the radiation projected onto the photosensitivematerial. The term “substantially opaque” means that the mask imageshould have a transmission optical density of about 2.0 or greater, moreparticularly about 3.0 or greater. The unmasked areas should besubstantially transparent. The term “substantially transparent” meansthat the unmasked areas of the photosensitive material should have atransmission optical density of about 0.5 or less, more particularlyabout 0.1 or less, even more particularly about 0.05 or less. Thetransmission optical density may be measured using a suitable filter ona densitometer, such as, for example a MACBETH TR 927.

This step is illustrated in FIGS. 1D and 3C. As described above, FIG. 1Dillustrates an embodiment in which the photosensitive material 10 isexposed to the curing radiation 14 after the carrier sheet 6 is removedfrom the mask image 4. In this embodiment, the photosensitive material10 is exposed to the curing radiation 14 through the mask image 4 afterthe carrier sheet 6 is removed. In another embodiment, illustrated inFIG. 3C, the photosensitive material 30 is exposed to a curing radiation34 through the mask image 24 before the carrier sheet 26 is removed.

Generally the step of exposing the photosensitive material through themask image may be done by floodwise exposure, since the mask imagepreferentially blocks the curing radiation. Floodwise exposure may beconducted in a vacuum or can be conducted outside of a vacuum, in otherwords, while the photosensitive element is in the presence ofatmospheric oxygen. The exposure without vacuum eliminates the steps ofvacuum draw-down time, and may produce sharper dots.

Some embodiments of the methods are suitable for making a reliefprinting plate, such as a flexographic printing plate, from a sheet-formphotosensitive element having a support and a layer of photosensitivematerial on the support. In the manufacture of a flexographic printingplate, one side of the photosensitive material is generally firstexposed to curing radiation through the support (known as“back-exposure”) to prepare a thin, uniform cured layer on the supportside of the photosensitive layer. The photosensitive element is thenexposed to curing radiation through the mask image, thereby causing thephotosensitive material to harden or cure in unmasked areas. Unexposedand uncured portions of the photosensitive material are then removed bya developing process, described below, leaving the cured portions whichdefine the relief printing surface.

The wavelength or range of wavelengths suitable as the curing radiationwill be dictated by the nature of the photosensitive material. In someembodiments, the curing radiation is ultraviolet radiation. Sources ofradiation for floodwise exposure to ultraviolet radiation areconventional. Examples of suitable visible or UV sources include carbonarcs, mercury-vapor arcs, fluorescent lamps, electron flash units, andphotographic flood lamps. Suitable sources of UV radiation includemercury-vapor lamps, particularly sun lamps.

One example of a suitable standard radiation source is the SYLVANIA 350BLACKLIGHT fluorescent lamp (FR 48T12/350 VL/VHO/180, 115 w) which has acentral wavelength of emission around 354 nm. Another example is theBURGESS EXPOSURE FRAME, Model 5K-3343VSII with ADDALUX 754-18017 lamp,available from Burgess Industries, Inc. (Plymouth, Minn.).

Other suitable ultraviolet radiation sources include platemakers whichare able to both expose the photosensitive material to radiation anddevelop the photosensitive material after radiation exposure. Examplesof suitable platemakers include KELLEIGH MODEL 310 PLATEMAKER availablefrom the Kelleigh Corporation (Trenton, N.J.) and the GPP500F PLATEPROCESSOR, available from Global Asia Limited (Hong Kong).

The time for exposure through the mask image will depend upon the natureand thickness of the photosensitive material and the source ofradiation. For example, in one embodiment a FLEXCEL-SRH plate precursor,available from Kodak Polychrome Graphics (Norwalk, Conn.) may be mountedon a KELLEIGH MODEL 310 PLATEMAKER available from the KelleighCorporation (Trenton, N.J.) and back-exposed to UV-A radiation throughthe support for 35 seconds to prepare a thin, uniform cured layer on thesupport side of the photosensitive layer. The mask image may then betransferred to the separation layer of the FLEXEL-SRH plate precursor,and the assembly may then be exposed to UV-A radiation through the maskimage for 14 minutes.

Developing the Imaged Article

Another step of the invention includes developing the photosensitivematerial and mask image to form a relief image. As illustrated in FIG.1E developing the imaged article serves to remove the uncured portionsof the photosensitive material 10, leaving the cured portions whichdefine the relief image on the photosensitive substrate 12. Generally,the mask image will also be developed away during this step.

In one embodiment, the step of developing includes washing thephotosensitive material and mask image with a suitable developer.Suitable developers may dissolve, disperse, or swell the unexposed areasof the photosensitive material and mask image. Development may becarried out at about room temperature. Suitable developers includeorganic solutions, water, aqueous or semi-aqueous solutions. If water isused, it may contain a surfactant. The developer should be selectedbased upon the chemical nature of the photosensitive material. Suitableorganic solution developers include aromatic or aliphatic hydrocarbonsand aliphatic or aromatic halohydrocarbon solutions, or mixtures of suchsolutions with suitable alcohols. Other organic solution developers havebeen disclosed in published German Application 38 28 551 and in U.S.Pat. No. 5,354,645 to Schober et al. Suitable semi-aqueous developersmay contain water and a water miscible organic solution and an alkalinematerial. Suitable aqueous developers usually contain water and analkaline material. Other suitable aqueous developer combinations aredescribed in U.S. Pat. No. 3,796,602 to Briney, et al. One suitablecommercially available developer is CYREL OPTISOL ROTARY PLATE WASHOUTSOLUTION, available from DuPont Corporation (Wilmington, Del.).

Mechanical development may also be suitable. Mechanical means fordevelopment may include scrubbing or brushing the photosensitivematerial and mask image to remove the uncured portions. Employingmechanical means in combination with solvent development is commonlypracticed.

Thermal methods of development are also suitable. One thermal method isreported, for example, in U.S. Published Application 2004/0048199 toSchadebrodt, et al. and the references discussed therein. Anotherthermal method, in which an absorbent layer is used to absorb thenon-exposed areas of the photosensitive material is reported in U.S.Pat. No. 5,175,072 to Martens, which is hereby incorporated byreference. Other methods of thermal development may also be suitable.

Post-development processing of the relief image may be suitable in somecircumstances. Typical post-development processing includes drying ofthe relief image to remove any excess solvent, and post-curing thephotosensitive material (such as by further exposing the relief image tocuring radiation) to cause further hardening or crosslinking of thephotosensitive material. Such post-development processing will befamiliar to those skilled in the art.

For example, the relief image may be blotted or wiped dry, and thendried in a forced air or infrared oven. Drying times and temperaturesmay vary. Suitable temperatures for oven drying may include, forexample, about 60° C.

Flexographic printing plates may be post-exposed to ensure that thephotopolymerization process is complete and that the plate will remainstable during printing and storage. This post-exposure step utilizes thesame radiation source as the exposure step described above.

Detackification (which can also be referred to as “light finishing”) mayalso be used if the surface is still tacky. Tackiness can be eliminatedby methods known in the art, such as, for example, treatment withbromine or chlorine solutions. Such treatments have been reported in,for example, U.S. Pat. No. 4,400,459 to Gruetzmacher, U.S. Pat. No.4,400,460 to Fickes et al., and German Patent 28 23 300. Detackificationmay also be accomplished by exposure to ultraviolet-visible radiation.

The resulting relief image may have a depth from about 2-40% of theoriginal thickness of the photosensitive material. Thus, if thethickness of the uncured photosensitive material is 1500 μm, the depthof the relief image may be about 500 μm. For a flexographic printingplate, the depth may be about 150-500 μm. For a PCB, the photosensitivematerial is completely removed, in either the exposed or unexposedareas, to reveal the metal layer beneath the photosensitive material.Thus, in a PCB, the depth of the relief depends upon the thickness ofthe photosensitive material disposed on the metal layer. The depth ofthe relief is the difference in thickness of the cured photosensitivematerial in the raised areas (also known as “image areas”) of the plate,and the thickness of the cured photosensitive material in the valleys ofthe plate where the photosensitive material was developed.

This invention may take on various modifications and alterations withoutdeparting from the spirit and scope thereof. It is to be understood thatthis invention may be suitably practiced in the absence of any elementnot specifically disclosed herein. In describing preferred embodimentsof the invention, specific terminology is used for the sake of clarity.The invention, however, is not intended to be limited to the specificterms so selected, and it is to be understood that each term so selectedincludes all technical equivalents that operate similarly.

EXAMPLES Description and sources of materials used in the Examples

AIRVOL 205—polyvinyl alcohol, as a 10% total solids solution in water,available from Air Products (Allentown, Pa.)

BUTVAR B-76—polyvinyl butyral resin, available from Solutia, Inc. (St.Louis, Mo.)

Carbon Black Millbase—a mixture of 47.52% carbon black, 47.52% BUTVARB-76, and 4.95% DISPERBYK 161, available from BYK-Chemie USA(Wallingford, Conn.) as a 20% total solids solution in a 50:50 solventmix of methyl ethyl ketone and Solvent PM

Cellulose Nitrate—available from Aldrich Chemical (Milwaukee, Wis.)

CYASORB IR 165—infrared dye, available from Cytec Industries, Inc. (WestPaterson, N.J.)

D99—IR dye YKR-2900, available from Mitsui, USA (New York, N.Y.)

FC 4432—10% NOVEC Fluorosurfactant, available from 3M Company (St. Paul,Minn.), in methyl ethyl ketone

FC 55/35/10—a fluorocarbon surfactant made of a 55:35:10 ratio mixtureof a terpolymer of a fluorinated acrylate, a short chain alkyl acrylate,and a polar monomer as a 7.5% total solids solution in methyl ethylketone unless otherwise indicated, available from 3M Company, (St. Paul,Minn.)

GANTREZ S97BF—a polymethyl vinyl ether/maleic anhydride copolymer as a10% total solids solution in water, available from InternationalSpecialty Products, Inc. (Wayne, N.J.)

HPA-1186—a dihydropyridine derivative available from St.-JeanPhotochemicals, Inc., (Quebec, Canada)

KEYPLAST Yellow—C.I. Disperse Yellow 3, available from Keystone AnilineCorporation (Chicago, Ill.)

METHOCEL A15LV—a methylcellulose, available from Dow Chemical (Midland,Mich.)

NEPTUN Black X60—C.I. Solvent Black 3, available from BASF Corporation(Charlotte, N.C.)

OPTISOL—washout solution, available from DuPont (Wilmington, Del.)

PC 364—Infrared dye with the following structure

PCA—a mixture of 70 wt % poly(methyl cyanoacrylate) and 30 wt %poly(ethyl cyanoacrylate) as a 10% total solids solution in acetone

Polyethylene Glycol 400—available from Aldrich Chemical (St. Louis, Mo.)

PVA 523—10% Polyvinyl Alcohol 523 in water, available from Air Products(Allentown, Pa.)

Red Shade Yellow Millbase—a mixture of 47.52% Red Shade Yellow pigment,47.52% BUTVAR B-76, and 4.95% DISPERBYK 161, available from BYK-Chemie(Wallingford, Conn.) as a 15% total solids solution in a 50:50 solventmix of methyl ethyl ketone and Solvent PM

SANTICIZER 160—a butyl benzyl polymer, available from Ferro Corporation(Walton Hills, Ohio)

Solvent PM—propylene glycol monomethyl ether, available from EastmanChemicals, (Kingsport, Tenn.)

TRITON X-100—a surfactant available from Rohm and Haas, (Philadelphia,Pa.) as a 10% total solids solution in water

Violet Black Millbase—MICROLITH Violet B-K, available from CibaSpecialty Chemicals (Tarrytown, N.Y.), as a 10% total solids solution inmethyl ethyl ketone

Example 1

A relief image was formed on a flexographic printing plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 1 using a #10 wound-wire coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form arelease layer.

TABLE 1 Components and amounts of release layer solution in Example 1Component Amount in grams PVA 523 50.0 TRITON X-100 1.0 de-ionized water39.0 n-propanol 10.0

A barrier layer solution of the components listed in Table 2 was mixedand applied to the release layer using a #10 wound-wire coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer.

TABLE 2 Components and amounts of barrier layer solution in Example 1Component Amount in grams PCA 42.43 PC 364 0.56 FC 4432 0.30 acetone46.51 cyclohexanone 10.20

An imageable layer solution of the components listed in Table 3 wasmixed and applied to the barrier layer using #20 wound-wire coating rod.The resulting article was heated in an 180° F. oven for 3 minutes toform an imageable layer on the barrier layer.

TABLE 3 Components and amounts of imageable layer solution in Example 1Component Amount in grams Carbon Black Millbase 27.93 Violet BlackMillbase 6.86 Red Shade Yellow Millbase 5.84 D99 1.00 FC 55/35/10 0.67n-ethylperfluorosulfonamide 0.74 HPA-1186 0.13 methyl ethyl ketone 21.98cyclohexanone 15.00 Solvent PM 20.00

The imageable layer was imaged using DESERTCAT 88 infrared imager,available from ECRM (Tewksbury, Mass.) emitting 830 nm radiation in theablation mode with a focus value of 1473, a magnification setting of510, and an energy level of 1.4 J/cm² to form an imaged film.

A CYREL analog flexographic precursor, 0.067 inch thick, available fromDuPont (Wilmington, Del.) containing a substrate, a curable material, ananti-tack layer, and a cover sheet, was back-exposed with UV-A radiationthrough the substrate for 120 seconds on a Burgess frame high setting.The cover sheet was then removed and the flexographic precursor wasplaced in a 100° C. oven for 3 minutes. While the flexographic precursorwas in the oven, the imaged film was laminated to the flexographicprecursor by contacting, face-to-face, the imaged imageable layer withthe anti-tack layer of the flexographic precursor using a hand held inkroller. The flexographic precursor and the imaged film were then removedfrom the oven and allowed to cool for 2 min. The carrier sheet was thenpeeled from the imaged imageable layer.

After the carrier sheet was peeled from the imaged imageable layer, theresulting assembly was mounted on the Burgess frame with the imagedimageable layer facing the source of the radiation and exposed to UVradiation for 600 seconds without vacuum draw-down to form an exposedflexographic precursor.

The exposed flexographic precursor was then placed in a pan and 50 ml ofOPTISOL was added. The exposed flexographic precursor was brushed withthe OPTISOL for 2 min. The exposed flexographic precursor was thenblotted dry, washed with water to remove the PVA, and then blotted dryagain. The exposed flexographic precursor was then placed back into thepan with the OPTISOL and brushed again. The brushing continued for 45minutes during which time the OPTISOL was replaced twice.

After washing and brushing, the exposed flexographic precursor was driedfor 2 hours in a 60° C. oven. The exposed flexographic precursor wasthen left to air dry for about 48 hours. After air drying, the exposedflexographic precursor was exposed to UV-C light for 8 minutes using aKELLEIGH MODEL 310 PLATEMAKER, available from Kelleigh Corporation(Trenton, N.J.) to form the relief image on the flexographic printingplate.

Example 2

A relief image on a flexographic printing plate was formed in the samemanner as in Example 1, except that the carrier sheet was removed fromthe imaged imageable layer after the flexographic precursor and imagedfilm were exposed to UV radiation rather than before the flexographicprecursor and imaged film were exposed to UV radiation.

The flexographic printing plates formed by the methods described inExample 1 and in Example 2 were used to print positive 3-point type.FIG. 5A shows an image of the type produced by the flexographic plateformed in Example 1 while FIG. 5B shows an image of the type produced bythe flexographic plate formed in Example 2.

The flexographic printing plates in Example 1 and in Example 2 were alsoused to print 30% dots. FIG. 6A shows an image of the 30% dots producedby the flexographic plate formed in Example 1 while FIG. 6B shows animage of the 30% dots produced by the flexographic plate formed inExample 2.

Example 3

A relief image was formed on a flexographic printing plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 4 using a #10 wire-wound coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form arelease layer.

TABLE 4 Components and amounts of release layer solution in Example 3Component Amount in grams METHOCEL A 15LV 3.2 TRITON X-100 1.0de-ionized water 70.8 n-propanol 25.0

A barrier layer solution of the components listed in Table 5 was mixedand applied to the release layer using a #10 wire-wound coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer.

TABLE 5 Components and amounts of barrier layer solution in Example 3Component Amount in grams PCA 42.43 PC 364 0.56 FC 4432 0.30 acetone46.51 cyclohexanone 10.20

An imageable layer solution of the components listed in Table 6 wasmixed and applied to the barrier layer using #20 wire-wound coating rod.The resulting article was heated in an 180° F. oven for 3 minutes toform an imageable layer on the barrier layer.

TABLE 6 Components and amounts of imageable layer solution in Example 3Component Amount in grams NEPTUN Black X60 0.96 KEYPLAST Yellow 2.52Cellulose Nitrate 3.68 D99 1.36 methyl isobutyl ketone 66.52 ethylalcohol 25.00

The imageable layer was then imaged with infrared radiation in themanner described in Example 1 to form an imaged film. The non-exposedareas of the imaged imageable layer exhibited a transmission opticaldensity of greater than 4.0, the areas exposed with 0.3 J/cm² infraredradiation exhibited a transmission optical density of 0.92, the areasexposed with 0.4 J/cm² infrared radiation exhibited a transmissionoptical density of 0.32, the areas exposed with 0.5 J/cm² infraredradiation exhibited a transmission optical density of 0.08, and theareas exposed with 0.6 J/cm² infrared radiation exhibited a transmissionoptical density of 0.04. The transmission optical densities weremeasured using a MACBETH TR 927 densitometer.

A FLEXCEL-SRH flexographic precursor (the “precursor”), available fromKodak Polychrome Graphics (Norwalk, Conn.), containing a substrate, acurable material, an anti-tack layer, and a cover sheet, wasback-exposed with UV-A radiation through the substrate on a KELLEIGHMODEL 310 PLATEMAKER for 35 seconds, and the cover sheet was peeled fromthe precursor. The imaged film was laminated to the precursor by placingthe precursor in the entrance to a KODAK MODEL 800XL APPROVAL LAMINATOR,available from Eastman Kodak Co. (Rochester, N.Y.), and placing theimaged film on the precursor with the imaged imageable layer facing theanti-tack layer of the precursor. The precursor and imaged film werethen laminated together with a surface interface temperature of about230° F. (110° C.) and a pressure of about 15 pounds per square inch (1kg/cm²). The laminator speed was set at 30 inches/minute (76.2cm/minute) resulting in a thermal dwell time of 48 seconds. Upon exitingthe laminator, the precursor and imaged film were air cooled for 3minutes. The carrier sheet was then peeled from the imaged imageablelayer.

After the carrier sheet was peeled from the imaged imageable layer, theresulting assembly was placed on the KELLEIGH MODEL 310 PLATEMAKER withthe imaged opaque layer facing the source of the radiation. Withoutusing a vacuum draw-down, the assembly was exposed to UV-A radiation for14 minutes to form an exposed precursor.

The exposed precursor was then developed for 20 minutes using OPTISOLsolution in the KELLEIGH MODEL 310 PLATEMAKER. After development, theprecursor was dried in a 140° F. oven for 2 hours and then placed backon the KELLEIGH MODEL 310 PLATEMAKER for light finishing with UV-Cradiation for 8 minutes. Finally, the precursor was post-exposed withUV-A radiation for 10 minutes to produce the relief image on theflexographic printing plate.

Example 4

A relief image was formed on a flexographic printing plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 7 using a #10 wound-wire coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form arelease layer.

TABLE 7 Components and amounts of release layer solution in Example 4Component Amount in grams METHOCEL A 15LV 3.2 TRITON X-100 1.0de-ionized water 70.8 n-propanol 25.0

A barrier layer solution of the components listed in Table 8 was mixedand applied to the release layer using a #10 wound-wire coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer.

TABLE 8 Components and amounts of barrier layer solution in Example 4Component Amount in grams PCA 42.43 CYASORB IR 165 0.56 FC 4432 0.30acetone 46.51 cyclohexanone 10.20

An imageable layer solution of the components listed in Table 9 wasmixed and applied to the barrier layer using a wound-wire coating rod toachieve a transmission optical density of 4.0. The resulting article washeated in an 180° F. oven for 3 minutes to form an imageable layer.

TABLE 9 Components and amounts of imageable layer solution in Example 4Component Amount in grams Carbon Black Millbase 32.86 Violet BlackMillbase 8.07 Red Shade Yellow Millbase 6.87 CYASORB IR 165 1.00 FC55/35/10 0.67 n-ethylperfluorosulfonamide 0.83 methyl ethyl ketone 19.51cyclohexanone 20.00 Solvent PM 10.00

The imageable layer was then imaged with infrared radiation with anEsko-Sparks laser imager, available from Esko-Graphics (Kennesaw, Ga.),with a wavelength of 1064 nm, to form an imaged film. The non-exposedareas of the imageable layer exhibited a transmission optical density ofgreater than 4.0, the areas exposed with 1.2 J/cm² infrared radiationexhibited a transmission optical density of 0.35, the areas exposed with1.55 J/cm² infrared radiation exhibited a transmission optical densityof 0.09, the areas exposed with 2.2 J/cm² infrared radiation exhibited atransmission optical density of 0.03, and the areas exposed with 3.3J/cm² infrared radiation exhibited a transmission optical density of0.03. The transmission optical densities was measured using a MACBETH TR927 densitometer.

The imaged film was then laminated to a FLEXCEL-SRH flexographicprecursor available from Kodak Polychrome Graphics (Norwalk, Conn.) andexposed to UV radiation in the manner described in Example 3 to producea relief image on the flexographic printing plate.

Example 5

A mask was formed on the surface of a flexographic plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 10 using a #10 wire-wound coating rod.The resulting article was heated in an 180° F. oven for 3 minutes toform a release layer.

TABLE 10 Components and amounts of release layer solution in Example 5Component Amount in grams PVA 523 50.00 TRITON X-100 1.0 de-ionizedwater 70.8 n-propanol 25.0

A barrier layer solution of the components listed in Table 11 was mixedand applied to the release layer using a #10 wire-wound coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer.

TABLE 11 Components and amounts of barrier layer solution in Example 5Component Amount in grams PCA 42.43 PC 364 0.56 FC 4432 0.30 acetone46.51 cyclohexanone 10.20

An imageable layer solution of the components listed in Table 12 wasmixed and applied to the barrier layer using a wound wire coating rod toform an imageable layer with a transmission optical density of 4.0.

TABLE 12 Components and amounts of imageable layer solution in Example 5Component Amount in grams Carbon Black Millbase 27.93 Violet BlackMillbase 6.86 Red Shade Violet Millbase 5.84 D99 1.0 FC 55/35/10 0.67methyl ethyl ketone 21.98 cyclohexanone 15.00 Solvent PM 20.00

An APPROVAL INTERMEDIATE RECEPTOR SHEET, available from Kodak PolychromeGraphics (Norwalk, Conn.), was placed in proximate contact with theimageable layer. The imageable layer was then imaged through the carriersheet on a DESERTCAT 88 imager using 830 nm radiation at 400 mJ usingvacuum hold-down. The approval intermediate receptor sheet received theimaged imageable material from the carrier sheet. The imaged imageablematerial on the approval intermediate receptor sheet was then laminatedonto a FLEXCEL-SRH flexographic precursor available from KodakPolychrome Graphics (Norwalk, Conn.) using a KODAK model 800XL APPROVALLAMINATOR. The reverse image remaining on the carrier sheet was alsolaminated to another FLEXCEL-SRH flexographic precursor available fromKodak Polychrome Graphics (Norwalk, Conn.) using a KODAK model 800XLAPPROVAL LAMINATOR.

Example 6

A first flexographic printing plate was made by the following process.An imaged film was made in the manner described in Example 1. The imagedfilm was then laminated to a CYREL analog flexographic precursor,available from DuPont (Wilmington, Del.), the carrier sheet was removedfrom the imaged imageable layer and the precursor was exposed to UVradiation and developed all in the manner described in Example 1. Theresulting relief image on the flexographic plate had a height of 22 mil.

A second flexographic printing plate was made by a known integral maskmethod. A commercially available sample of DuPont CDI digitalflexographic material, available from DuPont (Wilmington, Del.), waslaser exposed on the DESERTCAT 88 imager then exposed to UV radiationand developed as described in Example 1. The resulting relief image onthe flexographic plate had a height of 23 mil.

The first flexographic plate was then mounted on the plate cylinder of aMark Andy 2200F narrow-width flexographic press, available from MarkAndy, Inc. (St. Louis, Mo.) and used to process UV process black ink,available from Akzo Nobel, Inc. (Chicago, Ill.) onto 10 inch wideWestvaco #2 paper. The second flexographic plate was used in the samemanner as the first flexographic plate to print images using the sametype of paper, ink and using the same flexographic press. The printedimages produced by the first and second flexographic plates werecompared.

The spatial resolution in printed images from a flexographic plateproduced by a method of the invention is also better than the spatialresolution in images printed from a flexographic plate produced by aknown integral mask method. FIG. 7A, for example, shows a measured linewidth of 56 micrometers in a lower-case L in four-point Helvetica typeprinted by a flexographic plate produced by a method of the invention.FIG. 7B shows a measured line width of 81 micrometers in a lower-case Lin four-point Helvetica type printed by a flexographic plate produced bya known integral mask method.

The improved resolution of printing by a flexographic plate produced bya method of the invention is also illustrated by the narrower printedwidth of 80 micrometer fine lines. The fine lines printed from aflexographic plate produced by a known integral mask method, shown inFIG. 8B, were found to be approximately 40% wider than those printed bya flexographic plate produced by a method of the invention, shown inFIG. 8A.

Improved transmission of UV-A and visible light by an article producedby a method of the invention can be seen in FIGS. 9A, 9B, and 9C. FIG.9A shows 25% dots produced by a known Silver Halide mask, transmitting88%-90% of UV-A radiation. FIG. 9B shows 25% dots produced by anintegral mask method, transmitting 73%-78% of UV-A radiation. FIG. 9Cshows 25% dots produced by a mask image produced by a method of theinvention, transmitting 95%-98% of UV-A radiation.

Example 7

A relief image was formed on a flexographic printing plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 13 using a #10 wound-wire coating rod.The resulting article was heated in an 180° F. oven for 3 minutes toform a release layer on the carrier sheet.

TABLE 13 Components and amounts of the release layer solution in Example7 Component Amount in grams GANTREZ S97BF 28.5 AIRVOL 205 19.0 TRITONX-100 1.5 Polyethylene Glycol 400 0.25 de-ionized water 32.1 n-propanol20.0

A barrier layer solution of the components listed in Table 14 was mixedand applied to the release layer using a #10 wound-wire coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer on the release layer.

TABLE 14 Components and amounts of the barrier layer solution in Example7 Component Amount in grams PCA 44.5 D99 0.55 FC 55/35/10 (as a 10%total solids solution in methyl 0.40 ethyl ketone) acetone 5.0cyclohexanone 49.55

A solution of imageable material containing the components listed inTable 15 was mixed and applied to the barrier layer using #20 wound-wirecoating rod. The resulting article was heated in an 180° F. oven for 3minutes to form a layer of imageable material on the barrier layer.

TABLE 15 Components and amounts of the solution of imageable material inExample 7 Component Amount in grams NEPTUN Black X60 0.47 KEYPLASTYellow 1.60 curcumin 0.80 cellulose nitrate 2.74 BUTVAR B-76 (as a 10%total solids solution in 9.06 methyl ethyl ketone) D99 1.20 SANTICIZER160 0.36 methyl isobutyl ketone 58.77 ethyl alcohol 25.00

The layer of imageable material was imaged using DESERTCAT 88 infraredimager, available from ECRM (Tewksbury, Mass.) emitting 830 nm radiationin the ablation mode at an energy level of 0.7 J/cm² to form an imagedfilm.

A FLEXCEL-SRH flexographic precursor (the “precursor”), available fromKodak Polychrome Graphics (Norwalk, Conn.), containing a substrate, acurable material, an anti-tack layer, and a cover sheet, wasback-exposed with UV-A radiation through the substrate on a KELLEIGHMODEL 310 PLATEMAKER for 35 seconds, and the cover sheet was peeled fromthe precursor. The imaged film was laminated to the precursor by placingthe precursor in the entrance to a KODAK MODEL 800XL APPROVAL LAMINATOR,available from Eastman Kodak Co. (Rochester, N.Y.), and placing thearticle on the precursor with the imaged layer of imageable materialfacing the anti-tack layer of the precursor. The precursor and imagedfilm were then laminated together with a surface interface temperatureof about 230° F. (110° C.) and a pressure of about 15 pounds per squareinch (1 kg/cm²). The laminator speed was set at 30 inches/minute (76.2cm/minute) resulting in a thermal dwell time of 48 seconds. Upon exitingthe laminator, the precursor and imaged film were air cooled for 3minutes to form an assembly of the imaged film on the flexographicprecursor.

After cooling, the assembly was placed on the KELLEIGH MODEL 310PLATEMAKER with the imaged film facing the source of the radiation.Without using a vacuum draw-down, the assembly was exposed to UV-Aradiation for 13 minutes to form an exposed precursor.

Following exposure, the carrier sheet was removed by manually peelingthe carrier sheet from the remaining components of the imaged film.

The exposed precursor and remaining components of the imaged film werethen developed for 20 minutes using OPTISOL solution in the KELLEIGHMODEL 310 PLATEMAKER to form a relief image. After development, therelief image was dried in a 140° F. oven for 2 hours and then placedback on the KELLEIGH MODEL 310 PLATEMAKER for light finishing with UV-Cradiation for 8 minutes. Finally, the relief image was post-exposed withUV-A radiation for 10 minutes.

Example 8 Comparative

A relief image on a flexographic printing plate was formed in the samemanner as in Example 7, except that the assembly of the imaged film onthe flexographic precursor was exposed to UV radiation while in vacuumcontact with the FLEXCEL-SRH flexographic plate in the manner used withconventional silver halide masks.

The flexographic printing plates formed by the methods described inExample 7 and in Example 8 were examined microscopically at 75× usingback illumination. FIG. 10A shows an image of 4-point type produced inthe flexographic plate of Example 7 while FIG. 10B shows a digital imageof 4-point type produced in the flexographic plate of Example 8.

The digital images of small type produced from the transfer and contactmask exposures (shown in FIGS. 10A and 10B) show that the transferredmask is able to reproduce significantly sharper and distinct smalldetail compared with the contact mask exposure.

The flexographic printing plates of Examples 7 and 8 also contained3-point reversed type which was examined microscopically at 75× usingtop-surface illumination. FIG. 11A shows a photomicrograph of reversed3-point type produced in the flexographic plate of Example 7 while FIG.11B shows a photomicrograph of 3-point type produced in the flexographicplate of Example 8. Once again, the transferred mask reproducedsignificantly sharper small detail compared with the contact maskexposure.

Example 9

A relief image was formed on a flexographic printing plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 16 using a #10 wire-wound coating rod.The resulting article was heated in an 180° F. oven for 3 minutes toform a release layer on the carrier sheet.

TABLE 16 Components and amounts of the release layer solution in Example9 Component Amount in grams METHOCEL A 15LV 3.2 TRITON X-100 1.0de-ionized water 70.8 n-propanol 25.0

A barrier layer solution of the components listed in Table 17 was mixedand applied to the release layer using a #10 wire-wound coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer on the release layer.

TABLE 17 Components and amounts of the barrier layer solution in Example9 Component Amount in grams PCA 42.43 PC 364 0.56 FC 4432 0.30 acetone46.51 cyclohexanone 10.20

A solution of imageable material containing the components listed inTable 18 was mixed and applied to the barrier layer using #20 wire-woundcoating rod. The resulting article was heated in an 180° F. oven for 3minutes to form a layer of imageable material on the barrier layer.

TABLE 18 Components and amounts of the solution of imageable material inExample 9 Component Amount in grams NEPTUN Black X60 0.96 KEYPLASTYellow 2.52 cellulose nitrate 3.68 D99 1.36 methyl isobutyl ketone 66.52ethyl alcohol 25.00

The imageable material was then imaged with infrared radiation in themanner described in Example 7 to form an imaged film. The non-exposedareas of the imaged film exhibited a transmission optical density ofgreater than 4.0 and the areas exposed with 0.3 J/cm² infrared radiationexhibited a transmission optical density of 0.92, the areas exposed with0.4 J/cm² infrared radiation exhibited a transmission optical density of0.32, the areas exposed with 0.5 J/cm² infrared radiation exhibited atransmission optical density of 0.08 and the areas exposed with 0.6J/cm² infrared radiation exhibited a transmission optical density of0.04. The transmission optical densities were measured using a MACBETHTR 927 densitometer.

A FLEXCEL-SRH flexographic precursor (the “precursor”), available fromKodak Polychrome Graphics (Norwalk, Conn.), containing a substrate, acurable material, an anti-tack layer, and a cover sheet, wasback-exposed with UV-A radiation through the substrate on a KELLEIGHMODEL 310 PLATEMAKER for 35 seconds, and the cover sheet was peeled fromthe precursor. The imaged film was laminated to the precursor by placingthe precursor in the entrance to a KODAK MODEL 800XL APPROVAL LAMINATOR,available from Eastman Kodak Co. (Rochester, N.Y.), and placing thearticle on the precursor with the imaged layer of imageable materialfacing the anti-tack layer of the precursor. The precursor and imagedfilm were then laminated together with a surface interface temperatureof about 230° F. (110° C.) and a pressure of about 15 pounds per squareinch (1 kg/cm²). The laminator speed was set at 30 inches/minute (76.2cm/minute) resulting in a thermal dwell time of 48 seconds. Upon exitingthe laminator, the precursor and imaged film were air cooled for 3minutes to form an assembly of the imaged film on the flexographicprecursor.

After cooling, the assembly was placed on the KELLEIGH MODEL 310PLATEMAKER with the imaged film facing the source of the radiation.Without using a vacuum draw-down, the assembly was exposed to UV-Aradiation for 14 minutes to form an exposed precursor.

Following exposure, the carrier sheet was removed by manually peelingthe carrier sheet from the remaining components of the imaged film.

The exposed precursor and the remaining components of the imaged filmwere then developed for 20 minutes using OPTISOL solution in theKELLEIGH MODEL 310 PLATEMAKER to form a relief image. After development,the relief image was dried in a 140° F. oven for 2 hours and then placedback on the KELLEIGH MODEL 310 PLATEMAKER for light finishing with UV-Cradiation for 8 minutes. Finally, the relief image was post-exposed withUV-A radiation for 10 minutes.

Example 10

A relief image was formed on a flexographic printing plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 19 using a #10 wound-wire coating rod.The resulting article was heated in an 180° F. oven for 3 minutes toform a release layer.

TABLE 19 Components and amounts of the release layer solution in Example10 Component Amount in grams METHOCEL A 15LV 3.2 TRITON X-100 1.0de-ionized water 70.8 n-propanol 25.0

A barrier layer solution of the components listed in Table 20 was mixedand applied to the release layer using a #10 wound-wire coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer on the release layer.

TABLE 20 Components and amounts of barrier layer solution in Example 10Component Amount in grams PCA 42.43 CYASORB IR 165 0.56 FC 4432 0.30acetone 46.51 cyclohexanone 10.20

A solution of imageable material containing the components listed inTable 21 was mixed and applied to the barrier layer using a wound-wirecoating rod to achieve a transmission optical density of 4.0. Theresulting article was heated in an 180° F. oven for 3 minutes to form alayer of imageable material on the barrier layer.

TABLE 21 Components and amounts of the solution of imageable material inExample 10 Component Amount in grams Carbon Black Millbase 32.86 VioletBlack Millbase 8.07 Red Shade Yellow Millbase 6.87 CYASORB IR 165 1.00FC 55/35/10 0.67 n-ethylperfluorosulfonamide 0.83 methyl ethyl ketone19.51 cyclohexanone 20.00 Solvent PM 10.00

The layer of imageable material was then imaged with infrared radiationwith an Esko-Sparks laser imager, available from Esko-Graphics(Kennesaw, Ga.), with a wavelength of 1064 nm, to form an imaged film.The non-exposed areas of the imaged imageable material exhibited atransmission optical density of greater than 4.0 and the areas exposedwith 1.2 J/cm² infrared radiation exhibited a transmission opticaldensity of 0.35, the areas exposed with 1.55 J/cm² infrared radiationexhibited a transmission optical density of 0.09, the areas exposed with2.2 J/cm² infrared radiation exhibited a transmission optical density of0.03 and the areas exposed with 3.3 J/cm² infrared radiation exhibited atransmission optical density of 0.03. The transmission optical densitieswas measured using a MACBETH TR 927 densitometer.

The imaged film was then laminated to a FLEXCEL-SRH flexographicprecursor available from Kodak Polychrome Graphics (Norwalk, Conn.) andexposed to UV radiation and developed in the manner described in Example9 to produce a relief image on the flexographic printing plate.

Example 11

A mask was formed on the surface of a flexographic plate by thefollowing process. A carrier sheet, formed of 2 mil thick polyethyleneterephthalate, was coated with a release layer solution containing ofthe components listed in Table 22 using a #10 wire-wound coating rod.The resulting article was heated in an 180° F. oven for 3 minutes toform a release layer.

TABLE 22 Components and amounts of the release layer solution in Example11 Component Amount in grams PVA 523 50.00 TRITON X-100 1.0 de-ionizedwater 70.8 n-propanol 25.0

A barrier layer solution of the components listed in Table 23 was mixedand applied to the release layer using a #10 wire-wound coating rod. Theresulting article was heated in an 180° F. oven for 3 minutes to form abarrier layer on the release layer.

TABLE 23 Components and amounts of the barrier layer solution in Example11 Component Amount in grams PCA 42.43 PC 364 0.56 FC 4432 0.30 acetone46.51 cyclohexanone 10.20

A solution of imageable material containing the components listed inTable 24 was mixed and applied to the barrier layer using a wound wirecoating rod to form a layer of imageable material with a transmissionoptical density of 4.0 on the barrier layer.

TABLE 24 Components and amounts of the solution of imageable material inExample 11 Component Amount in grams Carbon Black Millbase 27.93 VioletBlack Millbase 6.86 Red Shade Violet Millbase 5.84 D99 1.0 FC 55/35/100.67 methyl ethyl ketone 21.98 cyclohexanone 15.00 Solvent PM 20.00

An approval intermediate receptor sheet, available from Kodak PolychromeGraphics (Norwalk, Conn.), was placed in proximate contact with thelayer of imageable material. The layer of imageable material was thenimaged through the carrier sheet on a DESERTCAT 88 imager using 830 nmradiation at 400 mJ using the vacuum hold-down. The approvalintermediate receptor sheet received the exposed imageable material fromthe carrier sheet. The imageable material on the approval intermediatereceptor sheet was then laminated onto a FLEXCEL-SRH flexographicprecursor available from Kodak Polychrome Graphics (Norwalk, Conn.)using a KODAK model 800XL APPROVAL LAMINATOR. The reverse imageremaining on the carrier sheet was also laminated to another FLEXCEL-SRHflexographic precursor available from Kodak Polychrome Graphics(Norwalk, Conn.) using a KODAK model 800XL APPROVAL LAMINATOR.

Example 12

A first flexographic printing plate was made by the following process.An imaged film was made, laminated to a FLEXCEL-SRH flexographicprecursor, available from Kodak Polychrome Graphics (Norwalk, Conn.),exposed to UV radiation and developed all in the manner described inExample 7. The resulting relief image on the flexographic plate had aheight of 23 mil.

A second flexographic printing plate was made by a known integral maskmethod. A commercially available sample of DuPont CDI digitalflexographic material, available from DuPont (Wilmington, Del.), waslaser exposed to 3.3 J/cm² of 830 nm radiation on the DESERTCAT 88imager then exposed to UV radiation and developed as described inExample 7. The resulting relief image on the flexographic plate had aheight of 23 mil.

The first flexographic plate was then mounted on the plate cylinder of aMark Andy 2200F narrow-width flexographic press, available from MarkAndy, Inc. (St. Louis, Mo.) and used to process UV process black ink,available from Akzo Nobel, Inc. (Chicago, Ill.) onto 10 inch wideWestvaco #2 paper. The second flexographic plate was used in the samemanner as the first flexographic plate to print images using the sametype of paper, ink and using the same flexographic press. The printedimages produced by the first and second flexographic plates werecompared.

The spatial resolution in printed images from a flexographic plateproduced by the first flexographic plate was measurably better than thatof images printed from the second flexographic plate produced by theintegral mask method. FIG. 12A, for example, shows a measured line widthof 56 micrometers for a lower-case L in four-point Helvetica typeprinted by first flexographic plate while FIG. 12B shows a measured linewidth of 78 micrometers for a lower-case L in four-point Helvetica typeprinted by the second flexographic plate.

The invention claimed is:
 1. A method of making a relief image, themethod comprising: (a) providing a film comprising an imageable materialdisposed on a carrier sheet; (b) contacting the imageable material witha receptor sheet; (c) forming a mask image on the receptor sheet byimagewise exposing the imageable material to infrared radiation to formexposed areas and transferring the exposed areas of the imageablematerial to the receptor sheet; (d) removing the carrier sheet from themask image; (e) transferring the mask image to a photosensitive materialthat is sensitive to a curing radiation; (f) exposing the photosensitivematerial to the curing radiation through the mask image to form animaged article, wherein the mask image is substantially opaque to thecuring radiation; and (g) developing the imaged article to form therelief image.
 2. The method of claim 1 wherein the receptor sheetcomprises a support having an image-receiving side and a non-image side,the image-receiving side comprises a polymer coating having a thicknessof from 2 μm to 20 μm.
 3. The method of claim 1 wherein the receptorsheet comprises a support having an image-receiving side and a non-imageside, the image-receiving side having a texturized surface.
 4. Themethod of claim 3 wherein the image-receiving side has a texturizedsurface provided by inert particulate material at a coverage of from 100to 500 particles/mm².
 5. The method of claim 1 wherein the step offorming the mask image on the receptor sheet comprises subliming acolorant in exposed areas to the receptor sheet.
 6. The method of claim1 wherein the step of forming the mask image on the receptor sheetcomprises ablating the exposed areas to the receptor sheet.
 7. Themethod of claim 1 wherein the step of forming the mask image on thereceptor sheet comprises melt-stick or laser-induced film transfer ofthe exposed areas of the imageable material to the receptor sheet. 8.The method of claim 1 further comprising the step of removing thereceptor sheet from the mask image.
 9. The method of claim 8 wherein thestep of removing the receptor sheet from the mask image occurs beforethe step of exposing the photosensitive material to the curingradiation.
 10. The method of claim 8 wherein the step of removing thereceptor sheet from the mask image occurs after the step of exposing thephotosensitive material to the curing radiation.
 11. The method of claim1 wherein the film further comprises a release layer disposed betweenthe carrier sheet and the imageable material.
 12. The method of claim 1wherein the film further comprises a barrier layer disposed between thecarrier sheet and the imageable material.
 13. The method of claim 12wherein the barrier layer comprises poly(cyanoacrylate alkyl) ornitrocellulose, and an infrared absorbing dye.
 14. The method of claim 1wherein the imageable material comprises an infrared absorber.
 15. Themethod of claim 1 wherein the imageable material comprises anultraviolet absorber.
 16. The method of claim 1 wherein the imageablematerial comprises a colorant.
 17. The method of claim 1 wherein theimageable material comprises an adhesive binder.
 18. The method of claim1 wherein the step of removing the carrier sheet from the mask imageoccurs before the step of exposing the photosensitive material to thecuring radiation.
 19. The method of claim 1 wherein the step of removingthe carrier sheet from the mask image occurs after the step of exposingthe photosensitive material to the curing radiation.
 20. The method ofclaim 1 for providing a flexographic printing plate wherein thephotosensitive material comprises a flexographic precursor thatcomprises an ultraviolet-curable material.
 21. The method of claim 1wherein the curing radiation comprises ultraviolet radiation.
 22. Themethod of claim 1 wherein the step of transferring the mask image to thephotosensitive material comprises laminating the mask image to thephotosensitive material.
 23. The method of claim 1 wherein the step ofexposing the photosensitive material to the curing radiation isperformed in ambient pressure, with or without heat.